JP2007265784A - Positive electrode active material for nonaqueous electrolyte secondary battery, its manufacturing method, and nonaqueous electrolyte secondary battery using it - Google Patents
Positive electrode active material for nonaqueous electrolyte secondary battery, its manufacturing method, and nonaqueous electrolyte secondary battery using it Download PDFInfo
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- JP2007265784A JP2007265784A JP2006088863A JP2006088863A JP2007265784A JP 2007265784 A JP2007265784 A JP 2007265784A JP 2006088863 A JP2006088863 A JP 2006088863A JP 2006088863 A JP2006088863 A JP 2006088863A JP 2007265784 A JP2007265784 A JP 2007265784A
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- Prior art keywords
- positive electrode
- active material
- lithium
- electrode active
- nickel
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- 239000007774 positive electrode material Substances 0.000 title claims abstract description 84
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 22
- 239000011255 nonaqueous electrolyte Substances 0.000 title claims description 38
- 239000002131 composite material Substances 0.000 claims abstract description 112
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims abstract description 88
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 claims abstract description 56
- UXZUCXCKBOYJDF-UHFFFAOYSA-N [Ti].[Co].[Ni] Chemical compound [Ti].[Co].[Ni] UXZUCXCKBOYJDF-UHFFFAOYSA-N 0.000 claims abstract description 52
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims abstract description 48
- 239000010936 titanium Substances 0.000 claims abstract description 41
- 239000007864 aqueous solution Substances 0.000 claims abstract description 36
- 229910000349 titanium oxysulfate Inorganic materials 0.000 claims abstract description 19
- 150000002642 lithium compounds Chemical class 0.000 claims abstract description 17
- 150000001868 cobalt Chemical class 0.000 claims abstract description 10
- 150000002815 nickel Chemical class 0.000 claims abstract description 10
- 239000000843 powder Substances 0.000 claims abstract description 10
- 239000012670 alkaline solution Substances 0.000 claims abstract description 8
- 238000004438 BET method Methods 0.000 claims description 29
- WSDFLEHAVFVYRT-UHFFFAOYSA-N [Ti].[Co].[Ni].[Li] Chemical compound [Ti].[Co].[Ni].[Li] WSDFLEHAVFVYRT-UHFFFAOYSA-N 0.000 claims description 28
- 238000010438 heat treatment Methods 0.000 claims description 22
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 9
- GLXDVVHUTZTUQK-UHFFFAOYSA-M lithium;hydroxide;hydrate Chemical compound [Li+].O.[OH-] GLXDVVHUTZTUQK-UHFFFAOYSA-M 0.000 claims description 8
- 239000011149 active material Substances 0.000 claims description 5
- 239000003792 electrolyte Substances 0.000 claims description 5
- SXGDIBYXFSKCRM-UHFFFAOYSA-L dilithium hydrogen carbonate hydroxide Chemical compound [OH-].[Li+].C([O-])(O)=O.[Li+] SXGDIBYXFSKCRM-UHFFFAOYSA-L 0.000 claims description 3
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 claims description 3
- 229910052808 lithium carbonate Inorganic materials 0.000 claims description 3
- 229940126062 Compound A Drugs 0.000 claims 1
- NLDMNSXOCDLTTB-UHFFFAOYSA-N Heterophylliin A Natural products O1C2COC(=O)C3=CC(O)=C(O)C(O)=C3C3=C(O)C(O)=C(O)C=C3C(=O)OC2C(OC(=O)C=2C=C(O)C(O)=C(O)C=2)C(O)C1OC(=O)C1=CC(O)=C(O)C(O)=C1 NLDMNSXOCDLTTB-UHFFFAOYSA-N 0.000 claims 1
- 229910052759 nickel Inorganic materials 0.000 abstract description 32
- 229910052719 titanium Inorganic materials 0.000 abstract description 22
- 229910052744 lithium Inorganic materials 0.000 abstract description 21
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 abstract description 20
- 239000000203 mixture Substances 0.000 abstract description 17
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 abstract description 16
- 229910017052 cobalt Inorganic materials 0.000 abstract description 12
- 239000010941 cobalt Substances 0.000 abstract description 12
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 abstract description 12
- 239000000243 solution Substances 0.000 abstract description 6
- 150000004679 hydroxides Chemical class 0.000 abstract description 4
- 229910052799 carbon Inorganic materials 0.000 abstract description 2
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 23
- 229910001416 lithium ion Inorganic materials 0.000 description 23
- 238000006243 chemical reaction Methods 0.000 description 18
- 238000011156 evaluation Methods 0.000 description 18
- 230000020169 heat generation Effects 0.000 description 16
- 238000002441 X-ray diffraction Methods 0.000 description 13
- -1 cobalt oxyhydroxide Chemical compound 0.000 description 13
- 238000000921 elemental analysis Methods 0.000 description 13
- 238000005259 measurement Methods 0.000 description 13
- 229910052782 aluminium Inorganic materials 0.000 description 12
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 11
- CKFRRHLHAJZIIN-UHFFFAOYSA-N cobalt lithium Chemical compound [Li].[Co] CKFRRHLHAJZIIN-UHFFFAOYSA-N 0.000 description 11
- 230000000052 comparative effect Effects 0.000 description 11
- 238000000034 method Methods 0.000 description 11
- 239000002245 particle Substances 0.000 description 11
- 239000011164 primary particle Substances 0.000 description 10
- 150000003839 salts Chemical class 0.000 description 10
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 9
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 9
- 238000010304 firing Methods 0.000 description 9
- 239000000463 material Substances 0.000 description 9
- 229910012851 LiCoO 2 Inorganic materials 0.000 description 8
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 8
- 239000011230 binding agent Substances 0.000 description 7
- 238000007600 charging Methods 0.000 description 7
- 238000000354 decomposition reaction Methods 0.000 description 7
- 230000001976 improved effect Effects 0.000 description 7
- RSNHXDVSISOZOB-UHFFFAOYSA-N lithium nickel Chemical compound [Li].[Ni] RSNHXDVSISOZOB-UHFFFAOYSA-N 0.000 description 7
- 239000011163 secondary particle Substances 0.000 description 7
- 239000002904 solvent Substances 0.000 description 7
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 6
- 230000007423 decrease Effects 0.000 description 6
- 229910052760 oxygen Inorganic materials 0.000 description 6
- 239000001301 oxygen Substances 0.000 description 6
- 238000000975 co-precipitation Methods 0.000 description 5
- RAHFUYKZTNGEBL-UHFFFAOYSA-F cobalt(2+) nickel(2+) titanium(4+) octahydroxide Chemical group [OH-].[Ti+4].[Co+2].[Ni+2].[OH-].[OH-].[OH-].[OH-].[OH-].[OH-].[OH-] RAHFUYKZTNGEBL-UHFFFAOYSA-F 0.000 description 5
- 239000008139 complexing agent Substances 0.000 description 5
- 239000008151 electrolyte solution Substances 0.000 description 5
- 150000003608 titanium Chemical class 0.000 description 5
- CPLXHLVBOLITMK-UHFFFAOYSA-N Magnesium oxide Chemical compound [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 4
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 4
- 239000000654 additive Substances 0.000 description 4
- 230000000996 additive effect Effects 0.000 description 4
- 238000002156 mixing Methods 0.000 description 4
- 239000003960 organic solvent Substances 0.000 description 4
- 239000002244 precipitate Substances 0.000 description 4
- LLZRNZOLAXHGLL-UHFFFAOYSA-J titanic acid Chemical compound O[Ti](O)(O)O LLZRNZOLAXHGLL-UHFFFAOYSA-J 0.000 description 4
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 3
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 3
- 239000002033 PVDF binder Substances 0.000 description 3
- 230000008901 benefit Effects 0.000 description 3
- 229910000361 cobalt sulfate Inorganic materials 0.000 description 3
- 229940044175 cobalt sulfate Drugs 0.000 description 3
- KTVIXTQDYHMGHF-UHFFFAOYSA-L cobalt(2+) sulfate Chemical compound [Co+2].[O-]S([O-])(=O)=O KTVIXTQDYHMGHF-UHFFFAOYSA-L 0.000 description 3
- 239000004020 conductor Substances 0.000 description 3
- 229910052802 copper Inorganic materials 0.000 description 3
- 239000010949 copper Substances 0.000 description 3
- 238000011161 development Methods 0.000 description 3
- 230000018109 developmental process Effects 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 230000007062 hydrolysis Effects 0.000 description 3
- 238000006460 hydrolysis reaction Methods 0.000 description 3
- 229910052742 iron Inorganic materials 0.000 description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 3
- 229910052748 manganese Inorganic materials 0.000 description 3
- 239000011572 manganese Substances 0.000 description 3
- 239000011259 mixed solution Substances 0.000 description 3
- 239000007773 negative electrode material Substances 0.000 description 3
- LGQLOGILCSXPEA-UHFFFAOYSA-L nickel sulfate Chemical compound [Ni+2].[O-]S([O-])(=O)=O LGQLOGILCSXPEA-UHFFFAOYSA-L 0.000 description 3
- 229910000363 nickel(II) sulfate Inorganic materials 0.000 description 3
- DCKVFVYPWDKYDN-UHFFFAOYSA-L oxygen(2-);titanium(4+);sulfate Chemical compound [O-2].[Ti+4].[O-]S([O-])(=O)=O DCKVFVYPWDKYDN-UHFFFAOYSA-L 0.000 description 3
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 238000006479 redox reaction Methods 0.000 description 3
- 238000005204 segregation Methods 0.000 description 3
- 239000002002 slurry Substances 0.000 description 3
- 235000011121 sodium hydroxide Nutrition 0.000 description 3
- 238000003860 storage Methods 0.000 description 3
- 238000006467 substitution reaction Methods 0.000 description 3
- 230000008093 supporting effect Effects 0.000 description 3
- 229910000348 titanium sulfate Inorganic materials 0.000 description 3
- 229910052720 vanadium Inorganic materials 0.000 description 3
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 2
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 description 2
- 229910000733 Li alloy Inorganic materials 0.000 description 2
- 229910013684 LiClO 4 Inorganic materials 0.000 description 2
- 229910015643 LiMn 2 O 4 Inorganic materials 0.000 description 2
- 229910013290 LiNiO 2 Inorganic materials 0.000 description 2
- 239000004698 Polyethylene Substances 0.000 description 2
- 239000004743 Polypropylene Substances 0.000 description 2
- WYURNTSHIVDZCO-UHFFFAOYSA-N Tetrahydrofuran Chemical compound C1CCOC1 WYURNTSHIVDZCO-UHFFFAOYSA-N 0.000 description 2
- PFYQFCKUASLJLL-UHFFFAOYSA-N [Co].[Ni].[Li] Chemical compound [Co].[Ni].[Li] PFYQFCKUASLJLL-UHFFFAOYSA-N 0.000 description 2
- KLARSDUHONHPRF-UHFFFAOYSA-N [Li].[Mn] Chemical compound [Li].[Mn] KLARSDUHONHPRF-UHFFFAOYSA-N 0.000 description 2
- 239000006230 acetylene black Substances 0.000 description 2
- 150000008044 alkali metal hydroxides Chemical class 0.000 description 2
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- 150000001869 cobalt compounds Chemical class 0.000 description 2
- 238000002485 combustion reaction Methods 0.000 description 2
- PQVSTLUFSYVLTO-UHFFFAOYSA-N ethyl n-ethoxycarbonylcarbamate Chemical compound CCOC(=O)NC(=O)OCC PQVSTLUFSYVLTO-UHFFFAOYSA-N 0.000 description 2
- 239000000706 filtrate Substances 0.000 description 2
- 239000011737 fluorine Substances 0.000 description 2
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- 229910003002 lithium salt Inorganic materials 0.000 description 2
- 159000000002 lithium salts Chemical class 0.000 description 2
- 229910052749 magnesium Inorganic materials 0.000 description 2
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- 229910052751 metal Inorganic materials 0.000 description 2
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- BFDHFSHZJLFAMC-UHFFFAOYSA-L nickel(ii) hydroxide Chemical compound [OH-].[OH-].[Ni+2] BFDHFSHZJLFAMC-UHFFFAOYSA-L 0.000 description 2
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- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- 229910021503 Cobalt(II) hydroxide Inorganic materials 0.000 description 1
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- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 description 1
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- 229910052718 tin Inorganic materials 0.000 description 1
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 1
- XJDNKRIXUMDJCW-UHFFFAOYSA-J titanium tetrachloride Chemical compound Cl[Ti](Cl)(Cl)Cl XJDNKRIXUMDJCW-UHFFFAOYSA-J 0.000 description 1
- DQWPFSLDHJDLRL-UHFFFAOYSA-N triethyl phosphate Chemical compound CCOP(=O)(OCC)OCC DQWPFSLDHJDLRL-UHFFFAOYSA-N 0.000 description 1
- 238000005303 weighing Methods 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
- 239000011701 zinc Substances 0.000 description 1
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Abstract
Description
本発明は、非水系電解質二次電池用正極活物質とその製造方法、および、これを用いた非水系電解質二次電池に関する。 The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, a method for producing the same, and a non-aqueous electrolyte secondary battery using the same.
近年、携帯電話やノート型パソコンなどの携帯電子機器の普及にともない、高いエネルギー密度を有する小型で軽量な非水系電解質二次電池の開発が強く望まれている。このような二次電池として、リチウムイオン二次電池がある。リチウムイオン二次電池の負極材料には、リチウム金属やリチウム合金、金属酸化物、あるいはカーボン等が用いられている。これらの材料は、リチウムを脱離および挿入することが可能な材料である。 In recent years, with the widespread use of portable electronic devices such as mobile phones and notebook computers, development of small and lightweight non-aqueous electrolyte secondary batteries having high energy density is strongly desired. As such a secondary battery, there is a lithium ion secondary battery. Lithium metal, lithium alloy, metal oxide, carbon, or the like is used as the negative electrode material of the lithium ion secondary battery. These materials are materials that can desorb and insert lithium.
このようなリチウムイオン二次電池については、現在、研究開発が盛んに行われているところである。この中でも、リチウム金属複合酸化物、特に合成が比較的容易なリチウムコバルト複合酸化物（ＬｉＣｏＯ2）を正極材料に用いたリチウムイオン二次電池は、４Ｖ級の高い電圧が得られるため、高いエネルギー密度を有する電池として実用化が進んでいる。このリチウムコバルト複合酸化物（ＬｉＣｏＯ2）を用いたリチウムイオン二次電池では、優れた初期容量特性やサイクル特性を得るための開発がこれまで数多く行われてきており、すでにさまざまな成果が得られている。 Research and development of such lithium ion secondary batteries is being actively conducted. Among these, a lithium ion secondary battery using a lithium metal composite oxide, particularly a lithium cobalt composite oxide (LiCoO 2 ), which is relatively easy to synthesize, as a positive electrode material can obtain a high voltage of 4 V, and thus has high energy. Practical use is progressing as a battery having a high density. In the lithium ion secondary battery using this lithium cobalt composite oxide (LiCoO 2 ), many developments have been made so far to obtain excellent initial capacity characteristics and cycle characteristics, and various results have already been obtained. ing.
しかし、リチウムコバルト複合酸化物（ＬｉＣｏＯ2）は、原料に希産で高価なコバルト化合物を用いているため、電池のコストアップの原因となる。このため、正極活物質として、リチウムコバルト複合酸化物（ＬｉＣｏＯ2）以外を用いることが望まれている。 However, since lithium cobalt complex oxide (LiCoO 2 ) uses a rare and expensive cobalt compound as a raw material, it causes an increase in battery cost. For this reason, it is desired to use materials other than lithium cobalt composite oxide (LiCoO 2 ) as the positive electrode active material.
また、最近は、携帯電子機器用の小型二次電池だけではなく、電力貯蔵用や、電気自動車用などの大型二次電池として、リチウムイオン二次電池を適用することへの期待も高まってきている。このため、正極材料のコストを下げ、より安価なリチウムイオン二次電池の製造を可能とすることは、広範な分野への大きな波及効果が期待できる。 Recently, not only small secondary batteries for portable electronic devices but also expectations for using lithium ion secondary batteries as large secondary batteries for power storage and electric vehicles are increasing. Yes. For this reason, reducing the cost of the positive electrode material and making it possible to manufacture a cheaper lithium ion secondary battery can be expected to have a large ripple effect in a wide range of fields.
リチウムイオン二次電池用正極活物質として新たに提案されている材料としては、コバルトよりも安価なマンガンを用いたリチウムマンガン複合酸化物（ＬｉＭｎ2Ｏ4）や、ニッケルを用いたリチウムニッケル複合酸化物（ＬｉＮｉＯ2）を挙げることができる。 Newly proposed materials as positive electrode active materials for lithium ion secondary batteries include lithium manganese composite oxide (LiMn 2 O 4 ) using manganese, which is cheaper than cobalt, and lithium nickel composite oxide using nickel. (LiNiO 2 ).
リチウムマンガン複合酸化物（ＬｉＭｎ2Ｏ4）は、原料が安価である上、熱安定性、特に、発火などについての安全性に優れるため、リチウムコバルト複合酸化物（ＬｉＣｏＯ2）の有力な代替材料であると言えるが、理論容量がリチウムコバルト複合酸化物（ＬｉＣｏＯ2）のおよそ半分程度しかないため、年々高まるリチウムイオン二次電池の高容量化の要求に応えるのが難しいという欠点を持っている。また、４５℃以上では、自己放電が激しく、充放電寿命も低下するという欠点も有している。 Lithium-manganese composite oxide (LiMn 2 O 4 ) is an effective alternative to lithium cobalt composite oxide (LiCoO 2 ) because it is inexpensive and has excellent thermal stability, especially safety with respect to ignition. However, since the theoretical capacity is only about half that of lithium cobalt composite oxide (LiCoO 2 ), it has a drawback that it is difficult to meet the demand for higher capacity of lithium ion secondary batteries that are increasing year by year. . Moreover, at 45 degreeC or more, it has the fault that self-discharge is intense and a charge / discharge lifetime also falls.
一方、リチウムニッケル複合酸化物（ＬｉＮｉＯ2）は、リチウムコバルト複合酸化物（ＬｉＣｏＯ2）とほぼ同じ理論容量を持ち、リチウムコバルト複合酸化物よりもやや低い電池電圧を示す。このため、電解液の酸化による分解が問題になりにくく、より高容量が期待できることから、開発が盛んに行われている。しかし、ニッケルを他の元素で置換せずに、純粋にニッケルのみで構成したリチウムニッケル複合酸化物を正極活物質として用いて、リチウムイオン二次電池を作製した場合、リチウムコバルト複合酸化物に比べ、サイクル特性が劣っている。また、高温環境下で使用されたり保存されたりした場合に、比較的電池性能を損ないやすいという欠点も有している。 On the other hand, lithium nickel composite oxide (LiNiO 2 ) has substantially the same theoretical capacity as lithium cobalt composite oxide (LiCoO 2 ), and shows a slightly lower battery voltage than lithium cobalt composite oxide. For this reason, decomposition | disassembly by oxidation of electrolyte solution does not become a problem, and development is performed actively from expecting higher capacity | capacitance. However, when a lithium-ion secondary battery is made using a lithium-nickel composite oxide composed purely of nickel as a positive electrode active material without replacing nickel with other elements, compared to lithium-cobalt composite oxide The cycle characteristics are inferior. In addition, when used or stored in a high temperature environment, the battery performance is relatively easily lost.
このような欠点を解決するために、例えば、特許文献１では、高温環境下での保存や使用に際して良好な電池性能を維持することのできる正極活物質として、ＬｉwＮｉxＣｏyＢzＯ2（０．０５≦ｗ≦１．１０、０．５≦ｘ≦０．９９５、０．００５≦ｚ≦０．２０、ｘ＋ｙ＋ｚ＝１）で表されるホウ素が添加されたリチウムニッケル複合酸化物が提案されている。
In order to solve such drawbacks, for example, in
また、特許文献２では、リチウムイオン二次電池の自己放電特性やサイクル特性を向上させることを目的として、ＬｉxＮｉaＣｏbＭcＯ2（０．８≦ｘ≦１．２、０．０１≦ａ≦０．９９、０．０１≦ｂ≦０．９９、０．０１≦ｃ≦０．３、０．８≦ａ＋ｂ＋ｃ≦１．２、Ｍは、Ａｌ、Ｖ、Ｍｎ、Ｆｅ、ＣｕおよびＺｎから選ばれる少なくとも１種の元素）で表されるリチウムニッケル系複合酸化物が提案されている。 Further, in Patent Document 2, Li x Ni a Co b M c O 2 (0.8 ≦ x ≦ 1.2, 0... Is intended to improve self-discharge characteristics and cycle characteristics of a lithium ion secondary battery. 01 ≦ a ≦ 0.99, 0.01 ≦ b ≦ 0.99, 0.01 ≦ c ≦ 0.3, 0.8 ≦ a + b + c ≦ 1.2, M is Al, V, Mn, Fe, Cu And at least one element selected from Zn) have been proposed.
しかしながら、これらの製造方法によって得られたリチウムニッケル系複合酸化物では、リチウムコバルト複合酸化物に比べて、充電容量および放電容量がともに高く、サイクル特性も改善されているが、満充電状態で高温環境下に放置しておくと、リチウムコバルト複合酸化物に比べて、低い温度から酸素放出を起こすといった問題がある。 However, the lithium nickel-based composite oxides obtained by these manufacturing methods have higher charge capacity and discharge capacity and improved cycle characteristics than the lithium cobalt composite oxide, but at high temperatures in a fully charged state. If left in the environment, there is a problem that oxygen is released from a lower temperature than lithium cobalt composite oxide.
このような問題を解決するために、例えば、特許文献３では、リチウムイオン二次電池正極材料の熱的安定性を向上させることを目的として、ＬｉaＭbＮｉcＣｏdＯe(Ｍは、Ａｌ、Ｍｎ、Ｓｎ、Ｉｎ、Ｆｅ、Ｖ、Ｃｕ、Ｍｇ、Ｔｉ、Ｚｎ、Ｍｏからなる群から選択される少なくとも一種の金属であり、かつ０＜ａ＜１．３、０．０２≦ｂ≦０．５、０．０２≦ｄ／ｃ＋ｄ≦０．９、１．８＜ｅ＜２．２の範囲であって、さらにｂ＋ｃ＋ｄ＝１である)で表されるリチウム含有複合酸化物等が提案されている。この場合に、添加元素Ｍとして、例えばアルミニウムを選択した場合、ニッケルからアルミニウムへの置換量を多くすれば、正極活物質の分解反応は抑えられ、熱安定性は向上することが確かめられている。しかし、十分な安定性を確保するのに有効なアルミニウムでニッケルを置換すると、充放電反応にともない、酸化還元反応に寄与するニッケルの量が減少するため、電池性能として最も重要である初期容量が大きく低下するという問題点を有している。これは、アルミニウムが３価で安定していることから、Ｒｅｄｏｘ反応に寄与しないために容量低下が起こるものと考えられる。
In order to solve such a problem, for example, in
また、特許文献４では、一般式ＬｉＮｉ1-xＣｏyＭzＯ2(ただし、０．１≦ｘ≦０．３、０．０５≦ｙ≦０．２８、０．０２≦ｚ≦０．２５、ｘ＝ｙ＋ｚであり、Ｍは、Ｍｇ、Ａｌ、Ｃａ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｆｅのうち少なくとも一種以上からなる)で表されるリチウム含有複合酸化物を、反応槽を用いて、これに塩濃度が調整されたニッケル−コバルト−Ｍ塩水溶液、その水溶液と錯塩を形成する錯化剤、および、アルカリ金属水酸化物をそれぞれ連続的に供給し、ニッケル−コバルト−Ｍ錯塩を生成させ、次いで、この錯塩をアルカリ金属水酸化物により分解して、ニッケル−コバルト−Ｍ水酸化物を析出させ、前記錯塩の生成および分解を槽内で循環させながら繰り返し行わせ、ニッケル−コバルト−Ｍ水酸化物をオ−バーフローさせて取り出すことにより得られる粒子形状が略球状であるニッケル−コバルト−Ｍ水酸化物を原料として用いて得るか、あるいは、さらにこれを焼成して、ニッケル−コバルト−Ｍ酸化物とした後に、これにリチウム塩を混合し、焼成して得ることが記載されている。 In Patent Document 4, the general formula LiNi 1-x Co y M z O 2 (where 0.1 ≦ x ≦ 0.3, 0.05 ≦ y ≦ 0.28, 0.02 ≦ z ≦ 0. 25, x = y + z, and M is composed of at least one of Mg, Al, Ca, Ti, V, Cr, Mn, and Fe) using a reaction vessel. In addition, a nickel-cobalt-M salt aqueous solution having a salt concentration adjusted thereto, a complexing agent that forms a complex salt with the aqueous solution, and an alkali metal hydroxide are continuously supplied to the nickel-cobalt-M complex salt. Next, the complex salt is decomposed with an alkali metal hydroxide to precipitate nickel-cobalt-M hydroxide, and the complex salt is repeatedly generated and decomposed while circulating in the tank. -M hydroxide overflow -After being obtained by using nickel-cobalt-M hydroxide having a substantially spherical particle shape as a raw material, or by firing it to obtain nickel-cobalt-M oxide It is described that a lithium salt is mixed and fired.
これは、水酸化ニッケルに二種以上の水酸化物を共沈させ、そのうちの一種をコバルトに限定することによって、リチウム含有複合酸化物の分極特性を改善し、さらにニッケルおよびコバルト以外の水酸化物を共沈させることにより、格子の安定化を図っている。この方法により得られた複合元素共沈水酸化物をリチウムイオン二次電池の正極活物質の材料として用いた場合、２元素共沈水酸化物であるコバルトニッケル水酸化物を用いた場合に比べ、初期容量が上昇し、また、充放電の繰り返しによるサイクル劣化が抑制されると記載されている。 This improves the polarization characteristics of lithium-containing composite oxides by coprecipitation of two or more hydroxides in nickel hydroxide and restricts one of them to cobalt. The lattice is stabilized by co-precipitation. When the composite element coprecipitated hydroxide obtained by this method is used as a material for the positive electrode active material of a lithium ion secondary battery, the initial value is compared with the case where cobalt nickel hydroxide which is a two element coprecipitated hydroxide is used. It is described that the capacity increases and cycle deterioration due to repeated charge and discharge is suppressed.
特許文献４の実施例５において、チタン塩として硫酸チタンを用いてニッケルコバルトチタン水酸化物であるＮｉ0.75Ｃｏ0.20Ｔｉ0.05（ＯＨ）2が作製されている。しかしながら、発明者らがこの水酸化物の作製を試みたところ、硫酸チタンは、３価ではほとんど水に不溶であり、４価では水溶性であるが、加水分解を起こしやすいことから、ニッケルコバルトチタン水溶液を用いて、安定してニッケルコバルトチタン水酸化物を得ることができず、チタン水酸化物が偏析し、また、粒成長がしにくくなり、工業的には不向きであることがわかった。 In Example 5 of Patent Document 4, Ni 0.75 Co 0.20 Ti 0.05 (OH) 2 that is nickel cobalt titanium hydroxide is produced using titanium sulfate as a titanium salt. However, when the inventors tried to produce this hydroxide, titanium sulfate is almost insoluble in water at trivalent and water-soluble at tetravalent, but it is susceptible to hydrolysis. It was found that nickel cobalt titanium hydroxide could not be stably obtained using titanium aqueous solution, titanium hydroxide segregated, and grain growth was difficult, which was not suitable for industrial use. .
最近では、携帯電子機器等の小型二次電池に対する高容量化の要求は年々高まる一方であり、安全性を確保するために容量を犠牲にすることは、リチウムニッケル複合酸化物による高容量化のメリットを失うことになる。また、リチウムイオン二次電池を大型二次電池に用いようという動きも盛んであり、中でもハイブリッド自動車用、電気自動車用の電源としての期待が大きい。したがって、自動車用の電源として用いられる場合、安全性に劣るというリチウムニッケル複合酸化物の問題点の解消は、大きな課題である。 Recently, the demand for higher capacity for small secondary batteries such as portable electronic devices has been increasing year by year, and sacrificing capacity to ensure safety is the result of higher capacity due to lithium nickel composite oxide. You will lose your benefits. In addition, a movement to use a lithium ion secondary battery for a large-sized secondary battery is also prominent. In particular, there is a great expectation as a power source for a hybrid vehicle and an electric vehicle. Therefore, when used as a power source for automobiles, solving the problem of the lithium nickel composite oxide that is inferior in safety is a big problem.
本発明は、かかる問題点に鑑みてなされたものであって、熱安定性が良好で、かつ高い充放電容量をもつ正極活物質を提供することを目的とする。 This invention is made | formed in view of this problem, Comprising: It aims at providing the positive electrode active material which has favorable thermal stability and has high charge / discharge capacity.
発明者等は、一般式Ｌｉ1+zＮｉ1-x-yＣｏxＭyＯ2（ただし、０．１０≦ｘ≦０．２１、０．０３≦ｙ≦０．０８、−０．０５≦ｚ≦０．１０）で表されるリチウムニッケルコバルト系複合酸化物の粉末について鋭意検討したところ、添加元素Ｍとしてチタンが、充電状態での熱安定性を向上させるのに好ましいとの知見を得た。 Inventors have general formula Li 1 + z Ni 1-xy Co x M y O 2 ( however, 0.10 ≦ x ≦ 0.21,0.03 ≦ y ≦ 0.08, -0.05 ≦ z As a result of intensive studies on the powder of lithium nickel cobalt composite oxide represented by ≦ 0.10), it was found that titanium is preferable as the additive element M for improving the thermal stability in the charged state. .
特に、均一なニッケルコバルトチタン系複合水酸化物を作製する点からは、添加チタン塩として硫酸チタニルを用いることが必要であることを見出した。 In particular, it has been found that it is necessary to use titanyl sulfate as the added titanium salt from the viewpoint of producing a uniform nickel cobalt titanium-based composite hydroxide.
また、ニッケル塩およびコバルト塩の混合水溶液と硫酸チタニルの硫酸水溶液にアルカリ溶液を加えて、ニッケルコバルトチタン水酸化物を共沈させ、得られたニッケルコバルトチタン複合水酸化物Ｎｉ1-x-yＣｏxＴｉy(ＯＨ)2とリチウム化合物とを混合し、６５０℃以上、８００℃以下の温度で熱処理することで得られる非水系電解質二次電池用正極活物質が、熱安定性が良好で、かつ、高い充放電容量をもつ正極活物質となることを見出した。 Further, an alkaline solution is added to a mixed aqueous solution of nickel salt and cobalt salt and a sulfuric acid aqueous solution of titanyl sulfate to coprecipitate nickel cobalt titanium hydroxide, and the resulting nickel cobalt titanium composite hydroxide Ni 1-xy Co x is obtained. A positive electrode active material for a non-aqueous electrolyte secondary battery obtained by mixing Ti y (OH) 2 and a lithium compound and heat-treating at a temperature of 650 ° C. or higher and 800 ° C. or lower has good thermal stability, and The present inventors have found that the positive electrode active material has a high charge / discharge capacity.
さらに、得られたニッケルコバルトチタン複合水酸化物Ｎｉ1-x-yＣｏxＴｉy(ＯＨ)2（ただし、０．１０≦ｘ≦０．２１、０．０３≦ｙ≦０．０８）を、３００℃以上、９００℃未満の温度で熱処理し、得られたニッケルコバルトチタン複合水酸化物とリチウム化合物とを混合し、６５０℃以上、８５０℃以下の温度で熱処理することで、比表面積が小さく、さらに熱安定性が向上することを見出し、本発明を完成するに至った。 Further, the obtained nickel cobalt titanium composite hydroxide Ni 1-xy Co x Ti y (OH) 2 (where 0.10 ≦ x ≦ 0.21, 0.03 ≦ y ≦ 0.08) was changed to 300 The specific surface area is small by heat-treating at a temperature not lower than 900 ° C and lower than 900 ° C, mixing the obtained nickel cobalt titanium composite hydroxide and the lithium compound, and heat-treating at a temperature not lower than 650 ° C and not higher than 850 ° C. Furthermore, it discovered that thermal stability improved and came to complete this invention.
すなわち、本発明の非水系電解質二次電池用正極活物質の製造方法は、リチウムニッケルコバルトチタン複合酸化物Ｌｉ1+zＮｉ1-x-yＣｏxＴｉyＯ2（ただし、０．１０≦ｘ≦０．２１、０．０３≦ｙ≦０．０８、−０．０５≦ｚ≦０．１０）の粉末からなる非水系電解質二次電池用正極活物質の製造方法に係る。 That is, the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention includes a lithium nickel cobalt titanium composite oxide Li 1 + z Ni 1-xy Co x Ti y O 2 (where 0.10 ≦ x ≦ 0.21, 0.03 ≦ y ≦ 0.08, −0.05 ≦ z ≦ 0.10). The present invention relates to a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery.
当該製造方法の特徴は、まず、ニッケルコバルトチタン複合水酸化物を得る工程において、ニッケル塩およびコバルト塩の混合水溶液と硫酸チタニルの硫酸水溶液に、アルカリ溶液を加え、５０℃以上、８０℃以下で、かつ、ｐＨ１０以上、ｐＨ１２．５以下の条件で、ニッケルコバルトチタン複合水酸化物を共沈させることに特徴がある。 The manufacturing method is characterized in that, in the step of obtaining a nickel cobalt titanium composite hydroxide, an alkaline solution is added to a mixed aqueous solution of nickel salt and cobalt salt and a sulfuric acid aqueous solution of titanyl sulfate at 50 ° C. or higher and 80 ° C. or lower. The nickel cobalt titanium composite hydroxide is co-precipitated under conditions of pH 10 or more and pH 12.5 or less.
また、得られたニッケルコバルトチタン複合水酸化物Ｎｉ1-x-yＣｏxＴｉy(ＯＨ)2（ただし、０．１０≦ｘ≦０．２１、０．０３≦ｙ≦０．０８）を、３００℃以上、９００℃未満の温度で熱処理し、得られたニッケルコバルトチタン複合酸化物をリチウム化合物と混合し、６５０℃以上、８５０℃以下の温度で熱処理することに特徴がある。 In addition, the obtained nickel cobalt titanium composite hydroxide Ni 1-xy Co x Ti y (OH) 2 (where 0.10 ≦ x ≦ 0.21, 0.03 ≦ y ≦ 0.08) was changed to 300 It is characterized in that it is heat-treated at a temperature not lower than 900 ° C. and lower than 900 ° C., and the obtained nickel cobalt titanium composite oxide is mixed with a lithium compound and heat-treated at a temperature not lower than 650 ° C. and not higher than 850 ° C.
なお、前記硫酸チタニルの硫酸水溶液には、硫酸が１０質量％以上である硫酸水溶液を用いることが望ましい。 The sulfuric acid aqueous solution of titanyl sulfate is preferably a sulfuric acid aqueous solution containing 10% by mass or more of sulfuric acid.
また、前記リチウム化合物には、炭酸リチウム、水酸化リチウム、炭酸リチウムの水和物、および、水酸化リチウムの水和物のいずれかを用いることが望ましい。 Moreover, it is desirable to use any of lithium carbonate, lithium hydroxide, lithium carbonate hydrate, and lithium hydroxide hydrate as the lithium compound.
本発明の非水系電解質二次電池用正極活物質は、前記のいずれかの非水系電解質二次電池用正極活物質の製造方法によって得られたリチウムニッケルコバルトチタン複合酸化物Ｌｉ1+zＮｉ1-x-yＣｏxＴｉyＯ2（ただし、０．１０≦ｘ≦０．２１、０．０３≦ｙ≦０．０８、−０．０５≦ｚ≦０．１０）の粉末からなる。 The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is a lithium nickel cobalt titanium composite oxide Li 1 + z Ni 1 obtained by any one of the above-described methods for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. It is made of a powder of -xy Co x Ti y O 2 (where 0.10 ≦ x ≦ 0.21, 0.03 ≦ y ≦ 0.08, −0.05 ≦ z ≦ 0.10).
当該正極活物質は、ＢＥＴ法で測定した比表面積が０．６ｍ2／ｇ以下であることが望ましい。 The positive electrode active material desirably has a specific surface area measured by the BET method of 0.6 m 2 / g or less.
本発明の非水系電解質二次電池は、本発明の非水系電解質二次電池用正極活物質を正極に用いることを特徴とする。 The non-aqueous electrolyte secondary battery of the present invention is characterized by using the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention as a positive electrode.
本発明の非水系電解質二次電池用正極活物質の製造方法により、工業的にリチウムニッケルコバルト複合酸化物からなる正極活物質を得ることができ、該正極活物質は、４価で安定するチタンで置換されることにより、ニッケルの一部が３価から２価となることで、ニッケルを別元素に置換したことによる電池の初期容量の低下を防止することができる。また、酸化力の強いチタンで置換させることで、リチウムイオン二次電池の正極として用いた場合、電池の熱安定性の向上を図ることができる。 According to the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, a positive electrode active material made of a lithium nickel cobalt composite oxide can be obtained industrially, and the positive electrode active material is tetravalent and stable titanium. By substituting with nickel, a part of the nickel is changed from trivalent to divalent, so that a decrease in the initial capacity of the battery due to the replacement of nickel with another element can be prevented. Further, by replacing with titanium having strong oxidizing power, when used as a positive electrode of a lithium ion secondary battery, it is possible to improve the thermal stability of the battery.
また、当該製造方法により、正極活物質の比表面積を小さくすることができ、電解液との反応面積を低減することで、電池の安全性を高められるという効果が付加される。また、二次粒子を形成している一次粒子が成長して、粒子の隙間を埋めることにより、タップ密度が向上し、電極としての充填密度が向上し、二リチウムイオン二次電池の実質的な容量アップにつながるという利点も有する。 In addition, the manufacturing method can reduce the specific surface area of the positive electrode active material, and can reduce the reaction area with the electrolytic solution, thereby adding the effect of improving the safety of the battery. Further, the primary particles forming the secondary particles grow and fill the gaps between the particles, thereby improving the tap density and the packing density as an electrode. There is also an advantage that the capacity is increased.
本発明の非水系電解質二次電池用正極活物質を用いて、非水系電解質二次電池を得ることにより、最近の携帯電子機器等の小型二次電池に対する高容量化の要求を満足するとともに、ハイブリッド自動車用や電気自動車用の大型二次電池に用いられる電源として求められる安全性をも確保することが可能となり、工業上、きわめて有用である。 By using the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention to obtain a non-aqueous electrolyte secondary battery, while satisfying the recent demand for higher capacity for small secondary batteries such as portable electronic devices, It is possible to ensure the safety required as a power source used for large-sized secondary batteries for hybrid vehicles and electric vehicles, which is extremely useful industrially.
本発明のリチウムイオン二次電池の実施形態について、各構成要素ごとにそれぞれ詳しく説明する。 Embodiments of the lithium ion secondary battery of the present invention will be described in detail for each component.
本発明のリチウムイオン二次電池は、正極、負極および非水系電解液などからなり、一般のリチウムイオン二次電池と同様の構成要素により構成される。なお、以下で説明する実施形態は例示に過ぎず、本発明の非水系電解質二次電池は、本明細書に記載されている実施形態を基に、当業者の知識に基づいて種々の変更、改良を施した形態で実施することができる。また、本発明の非水系電解質二次電池は、その用途を特に限定するものではない。 The lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, a non-aqueous electrolyte, and the like, and includes the same components as a general lithium ion secondary battery. The embodiment described below is merely an example, and the nonaqueous electrolyte secondary battery of the present invention can be variously modified based on the knowledge of those skilled in the art based on the embodiment described in the present specification. It can be implemented in an improved form. Moreover, the use of the nonaqueous electrolyte secondary battery of the present invention is not particularly limited.
（１）正極活物質、正極
本発明の非水系電解質二次電池用正極活物質は、一般式Ｌｉ1+zＮｉ1-x-yＣｏxＴｉyＯ2（ただし、０．１０≦ｘ≦０．２１、０．０３≦ｙ≦０．０８、−０．０５≦ｚ≦０．１０）で表されるリチウムニッケルコバルトチタン複合酸化物の粉末からなる。
(1) Positive electrode active material, positive electrode The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention has a general formula of Li 1 + z Ni 1-xy Co x Ti y O 2 (where 0.10 ≦ x ≦ 0. 21, 0.03 ≦ y ≦ 0.08, −0.05 ≦ z ≦ 0.10).
本発明による二次電池の充放電反応は、正極活物質内のリチウムイオンが可逆的に出入りすることで進行する。充電によってリチウムが引き抜かれた正極活物質は、高温で不安定であり、加熱すると活物質が分解して酸素を放出し、この酸素が電解液の燃焼を引き起こし、発熱反応が起こる。したがって、正極材料の熱安定性を改善するということは、リチウムが引き抜かれた正極活物質の分解反応を抑えるということである。 The charge / discharge reaction of the secondary battery according to the present invention proceeds by reversibly entering and exiting lithium ions in the positive electrode active material. The positive electrode active material from which lithium has been extracted by charging is unstable at high temperatures, and when heated, the active material decomposes and releases oxygen, which causes combustion of the electrolyte solution and causes an exothermic reaction. Therefore, improving the thermal stability of the positive electrode material means suppressing the decomposition reaction of the positive electrode active material from which lithium has been extracted.
従来、開示されている正極活物質の分解反応を抑える方法としては、アルミニウムのように、酸素との共有結合性の強い元素で、ニッケルの一部を置換することが一般的に行なわれてきた。確かに、ニッケルからアルミニウムへの置換量を多くすれば、正極活物質の分解反応は抑えられ、熱安定性が向上するが、充放電反応にともなう酸化還元反応に寄与するニッケルの量が減少することで、充放電容量の低下を招くため、アルミニウムへの置換量はある程度に留めなければならなかった。その結果、十分な熱安定性を確保した場合には、十分な可逆容量を得ることができず、ある程度の容量を得るためには、熱安定性を犠牲にしなければならなかった。 Conventionally, as a method for suppressing the decomposition reaction of the positive electrode active material disclosed, it has been generally performed to replace a part of nickel with an element having a strong covalent bond with oxygen such as aluminum. . Certainly, if the substitution amount from nickel to aluminum is increased, the decomposition reaction of the positive electrode active material is suppressed and the thermal stability is improved, but the amount of nickel contributing to the oxidation-reduction reaction accompanying the charge / discharge reaction is reduced. As a result, the charge / discharge capacity is reduced, so that the amount of substitution with aluminum has to be limited to some extent. As a result, when sufficient thermal stability was ensured, sufficient reversible capacity could not be obtained, and thermal stability had to be sacrificed in order to obtain a certain level of capacity.
このため、本発明では、一般式Ｌｉ1+zＮｉ1-x-yＣｏxＭyＯ2（ただし、０．１０≦ｘ≦０．２１、０．０３≦ｙ≦０．０８、−０．０５≦ｚ≦０．１０）で表されるリチウム金属複合酸化物の粉末において、添加元素Ｍとして、４価で安定するチタンを採用し、チタンで置換することで、ニッケルの一部が３価から２価となり、ニッケルを別元素に置換したことによる電池の初期容量の低下を防止するとともに、熱安定性の向上を図っている。 Therefore, in the present invention, the general formula Li 1 + z Ni 1-xy Co x M y O 2 ( however, 0.10 ≦ x ≦ 0.21,0.03 ≦ y ≦ 0.08, -0.05 In the lithium metal composite oxide powder represented by ≦ z ≦ 0.10), tetravalent and stable titanium is adopted as the additive element M, and a part of nickel is changed from trivalent by substituting with titanium. It is divalent and prevents a decrease in the initial capacity of the battery due to the replacement of nickel with another element, and also improves the thermal stability.
次に、本発明の非水系電解質二次電池用正極活物質の製造方法について説明する。 Next, the manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries of this invention is demonstrated.
本発明では、一般式Ｌｉ1+zＮｉ1-x-yＣｏxＴｉyＯ2（ただし、０．１０≦ｘ≦０．２１、０．０３≦ｙ≦０．０８、−０．０５≦ｚ≦０．１０）で表される層状構造を有するリチウムニッケルコバルトチタン複合酸化物を次のように製造する。 In the present invention, the general formula Li 1 + z Ni 1-xy Co x Ti y O 2 (where 0.10 ≦ x ≦ 0.21, 0.03 ≦ y ≦ 0.08, −0.05 ≦ z ≦ 0.10), a lithium nickel cobalt titanium composite oxide having a layered structure is produced as follows.
まず、コバルトとニッケルとチタンとの原子比が、前記一般式の原子比となるように、ニッケル塩とコバルト塩の混合水溶液と硫酸チタニルの硫酸水溶液を準備する。ニッケル塩とコバルト塩の混合水溶液と硫酸チタニルの硫酸水溶液にアルカリ溶液を加えて、それらを一定速度にて攪拌して、共沈殿させる。そして、定常状態になった後に、沈殿物を採取し、濾過し、水洗して、ニッケルコバルトチタン複合水酸化物を得る。 First, a mixed aqueous solution of nickel salt and cobalt salt and a sulfuric acid aqueous solution of titanyl sulfate are prepared so that the atomic ratio of cobalt, nickel, and titanium is the atomic ratio of the above general formula. An alkaline solution is added to a mixed aqueous solution of nickel salt and cobalt salt and a sulfuric acid aqueous solution of titanyl sulfate, and they are stirred at a constant speed to cause coprecipitation. And after becoming a steady state, a deposit is extract | collected, filtered, and washed with water, and nickel cobalt titanium composite hydroxide is obtained.
その後、得られたニッケルコバルトチタン複合水酸化物を３００℃以上、９００℃未満の温度で熱処理することによって、二次粒子を形成している一次粒子の成長を促し、比表面積を低減させるとともに、粒子同士の隙間を低減させることで、タップ密度の向上を図る。その上で、ニッケルコバルトチタン複合水酸化物を熱処理することで得られたニッケルコバルトチタン複合酸化物を、リチウム化合物と混合して、熱処理することで、望まれる比率のリチウムイオン二次電池用正極活物質として有用なリチウムニッケルコバルトチタン複合酸化物を得ている。 Thereafter, the obtained nickel cobalt titanium composite hydroxide is heat-treated at a temperature of 300 ° C. or higher and lower than 900 ° C., thereby promoting the growth of primary particles forming secondary particles, reducing the specific surface area, The tap density is improved by reducing the gap between the particles. Then, the nickel cobalt titanium composite oxide obtained by heat treating the nickel cobalt titanium composite hydroxide is mixed with the lithium compound and heat treated, so that the positive electrode for the lithium ion secondary battery in a desired ratio is obtained. A lithium nickel cobalt titanium composite oxide useful as an active material has been obtained.
本発明では、均一なニッケルコバルトチタン水酸化物を作製する点から、チタン塩として、硫酸チタニルを用いる。チタン塩として、塩化チタンや硫酸チタンを用いた場合、ニッケル塩およびコバルト塩との混合水溶液を作成する際に、加水分解あるいはその時点で酸化が進み、水酸化チタンあるいは酸化チタンが発生し、チタンの偏析が起きてしまう。また、粒成長がしにくくなり、工業的に不向きである。したがって、使用するチタン塩としては、水への溶解度の高い硫酸チタニルを用い、かつ、硫酸水溶液であることが工業的に必要となる。 In the present invention, titanyl sulfate is used as the titanium salt from the viewpoint of producing a uniform nickel cobalt titanium hydroxide. When titanium chloride or titanium sulfate is used as the titanium salt, when preparing a mixed aqueous solution with nickel salt and cobalt salt, hydrolysis or oxidation proceeds at that time, and titanium hydroxide or titanium oxide is generated. Segregation occurs. Moreover, it becomes difficult to grow grains and is not industrially suitable. Therefore, as the titanium salt to be used, it is industrially necessary to use titanyl sulfate having high solubility in water and to be an aqueous sulfuric acid solution.
また、本発明では、ニッケル塩およびコバルト塩の複合水溶液と硫酸チタニルの硫酸水溶液を準備し、ニッケル塩およびコバルト塩の混合水溶液と硫酸チタニルの硫酸水溶液にアルカリ溶液を加えて、それらを一定速度にて攪拌して、反応槽内にニッケルとコバルトとチタンとの原子比が、前記一般式の原子比となるように、ニッケルコバルトチタン複合水酸化物を共沈させる。そして、定常状態になった後に沈殿物を採取し、濾過し、水洗して、ニッケルコバルトチタン複合水酸化物を得ている。この工程により、３元素が均一に分散した複合水酸化物を得ることができる。 Further, in the present invention, a composite aqueous solution of nickel salt and cobalt salt and a sulfuric acid aqueous solution of titanyl sulfate are prepared, an alkaline solution is added to a mixed aqueous solution of nickel salt and cobalt salt and a sulfuric acid aqueous solution of titanyl sulfate, and these are made constant speed. The nickel-cobalt-titanium composite hydroxide is coprecipitated so that the atomic ratio of nickel, cobalt, and titanium is the atomic ratio of the above general formula. Then, after reaching a steady state, a precipitate is collected, filtered, and washed with water to obtain a nickel cobalt titanium composite hydroxide. By this step, a composite hydroxide in which the three elements are uniformly dispersed can be obtained.
リチウム化合物としては、炭酸リチウム、水酸化リチウム、炭酸リチウムの水和物、または、水酸化リチウムの水和物を用いることが好ましい。 As the lithium compound, lithium carbonate, lithium hydroxide, lithium carbonate hydrate, or lithium hydroxide hydrate is preferably used.
また、ニッケル化合物としては、硫酸ニッケル、酸化ニッケル、炭酸ニッケル、硝酸ニッケル、水酸化ニッケル、オキシ水酸化ニッケル等を使用することができる。コバルト化合物としては、硫酸コバルト、酸化コバルト、炭酸コバルト、硝酸コバルト、水酸化コバルト、オキシ水酸化コバルト等を使用することができる。 As the nickel compound, nickel sulfate, nickel oxide, nickel carbonate, nickel nitrate, nickel hydroxide, nickel oxyhydroxide, or the like can be used. As the cobalt compound, cobalt sulfate, cobalt oxide, cobalt carbonate, cobalt nitrate, cobalt hydroxide, cobalt oxyhydroxide and the like can be used.
ニッケル、コバルトおよびチタンの添加元素に係る化合物としては、酸化物、炭酸化物等を使用できるが、上述のように、複合水酸化物や複合酸化物を使用した方がより好ましい。 As the compounds related to the additive elements of nickel, cobalt and titanium, oxides, carbonates and the like can be used, but as described above, it is more preferable to use composite hydroxides or composite oxides.
また、硫酸チタニルは、硫酸が１０質量％以上であることが好ましい。硫酸が１０質量％未満では、保存中に加水分解を起こし、水酸化チタンが析出し、ニッケルコバルトチタン複合水酸化物を作製した場合、チタンの偏析が起こり、工業上、好ましくない。一方、市販の硫酸チタニルの硫酸濃度は３０〜５０％であるため、原液のままの使用であれば５０％程度の濃度での使用が可能である。 The titanyl sulfate preferably contains 10% by mass or more of sulfuric acid. When the sulfuric acid is less than 10% by mass, hydrolysis occurs during storage, titanium hydroxide is precipitated, and nickel cobalt titanium composite hydroxide is produced, which causes segregation of titanium, which is not industrially preferable. On the other hand, since the sulfuric acid concentration of commercially available titanyl sulfate is 30 to 50%, it can be used at a concentration of about 50% if it is used as it is.
本発明では、従来の方法と異なり、チタン溶液の添加をニッケル塩やコバルト塩の混合水溶液と別としている。その理由は、硫酸チタニルの硫酸水溶液と、その他の混合水溶液を最初に混合してしまうと、硫酸濃度の低下によりチタンの加水分解が起こり、チタンの偏析が起こる可能性があるためと、チタン水酸化物は両性で、酸やアルカリで再溶解するため、反応液中の硫酸および苛性ソーダが、析出したチタン水酸化物の再溶解に消費され、ニッケルおよびコバルトの析出を阻害し、粒子の成長が促進されず、微粉になりやすいためである。 In the present invention, unlike the conventional method, the addition of the titanium solution is separated from the mixed aqueous solution of nickel salt and cobalt salt. The reason for this is that if a sulfuric acid aqueous solution of titanyl sulfate and another mixed aqueous solution are first mixed, titanium may be hydrolyzed due to a decrease in sulfuric acid concentration, and segregation of titanium may occur. Since the oxide is amphoteric and re-dissolved with acid and alkali, sulfuric acid and caustic soda in the reaction solution are consumed for re-dissolution of the precipitated titanium hydroxide, hindering the precipitation of nickel and cobalt, and particle growth. It is because it is not promoted and tends to become fine powder.
反応条件は、錯化剤の使用の有無により異なるが、５０℃以上、８０℃以下の温度範囲で、混合水溶液がｐＨ１０以上、ｐＨ１２．５以下の範囲となるようにアルカリ溶液を添加して共沈殿させる。所定の条件下で一定速度にて攪拌し、反応槽内が定常状態になった後に、オーバーフローした沈殿物を採取し、濾過し、水洗して、ニッケルコバルトチタン複合水酸化物からなる粒子を得ることができる。 The reaction conditions vary depending on the presence or absence of the use of a complexing agent, but in the temperature range of 50 ° C. to 80 ° C., an alkaline solution is added so that the mixed aqueous solution has a pH of 10 to 12.5. Precipitate. After stirring at a constant speed under predetermined conditions and the inside of the reaction vessel is in a steady state, the overflowed precipitate is collected, filtered and washed with water to obtain particles made of nickel cobalt titanium composite hydroxide be able to.
ｐＨ領域は、錯化剤がない場合、ｐＨ１０以上、ｐＨ１１以下の範囲を選択し、かつ、混合水溶液の温度を６０℃以上、８０℃以下の範囲とする。錯化剤がない場合、ｐＨ１１より高く、特にｐＨ１３程度で晶析すると、細かい粒子となり、濾過性も悪くなり、球状粒子が得られない。また、ｐＨが１０よりも低いと、水酸化物の生成速度が著しく遅くなり、濾液中にニッケルが残留し、ニッケルの沈殿量が目的組成からずれて、目的の比率のニッケルコバルトチタン複合水酸化物が得られなくなってしまう。ｐＨ１０以上、ｐＨ１１以下とし、かつ、混合水溶液の温度を６０℃以上に保つことによって、すなわち、反応温度を上げ、またニッケルの溶解度を上げることによって、ニッケルの沈殿量が目的組成からずれて共沈にならない現象を回避している。 When there is no complexing agent, the pH range is selected in the range of pH 10 or more and pH 11 or less, and the temperature of the mixed aqueous solution is set in the range of 60 ° C. or more and 80 ° C. or less. In the absence of a complexing agent, crystallization at a pH higher than 11, particularly about pH 13, results in fine particles, poor filterability, and spherical particles cannot be obtained. On the other hand, if the pH is lower than 10, the hydroxide formation rate is remarkably slow, nickel remains in the filtrate, the amount of nickel precipitation deviates from the target composition, and the nickel cobalt titanium composite hydroxide of the target ratio. Things can no longer be obtained. By adjusting the pH of the mixed aqueous solution to 60 ° C. or higher by adjusting the pH of the mixed aqueous solution to 60 ° C. or higher, that is, by increasing the reaction temperature and increasing the solubility of nickel, the amount of nickel precipitates deviates from the target composition and coprecipitates. The phenomenon that does not become is avoided.
なお、混合水溶液の温度が８０℃を超えると、水の蒸発量が多いためにスラリー濃度が高くなり、ニッケルの溶解度が低下する上、濾液中に硫酸ナトリウム等の結晶が発生し、不純物濃度が上昇する等、正極材料の充放電容量が低下する原因となる状態が起こるので、好ましくない。 When the temperature of the mixed aqueous solution exceeds 80 ° C., the amount of water evaporation increases, so that the slurry concentration increases, the solubility of nickel decreases, crystals such as sodium sulfate are generated in the filtrate, and the impurity concentration increases. Since a state that causes a decrease in charge / discharge capacity of the positive electrode material occurs, such as an increase, it is not preferable.
アンモニアなど錯化剤を使用する場合には、ニッケルの溶解度が上昇するため、ｐＨ領域をｐＨ１０以上、１２．５以下、温度領域も５０℃〜８０℃まで、それぞれ広げることができる。 When a complexing agent such as ammonia is used, the solubility of nickel increases, so that the pH range can be expanded to pH 10 or more and 12.5 or less, and the temperature range can be expanded to 50 ° C. to 80 ° C., respectively.
以上により、ニッケルとコバルトとチタンの原子比が、望む比率に均一に混合された粒子を得ることができる。さらに、得られる粒子は球状に近く、濾過性も良好で、実にハンドリング性の良い良好な粒子が得られる。なお、ニッケルコバルトチタン複合水酸化物は、１μｍ以下の一次粒子が複数集合した球状の二次粒子からなることが好ましい。 As described above, particles in which the atomic ratio of nickel, cobalt, and titanium is uniformly mixed in a desired ratio can be obtained. Furthermore, the obtained particles are nearly spherical, have good filterability, and give good particles with good handling properties. The nickel cobalt titanium composite hydroxide is preferably composed of spherical secondary particles in which a plurality of primary particles of 1 μm or less are aggregated.
その後、得られたニッケルコバルトチタン複合水酸化物を、３００℃以上、９００℃未満の温度で熱処理し、得られたニッケルコバルトチタン複合酸化物とリチウム化合物とを混合し、６５０℃以上、８５０℃以下の温度で熱処理する。 Thereafter, the obtained nickel cobalt titanium composite hydroxide is heat-treated at a temperature of 300 ° C. or more and less than 900 ° C., and the obtained nickel cobalt titanium composite oxide and the lithium compound are mixed, and 650 ° C. or more and 850 ° C. Heat treatment is performed at the following temperature.
得られたニッケルコバルトチタン複合水酸化物は、３００℃以上、９００℃未満の温度で熱処理することが必要である。熱処理温度は、７５０℃〜８００℃がさらに好ましい。熱処理温度が９００℃以上であると、複合水酸化物が酸化物に変化した後の粒成長が著しく、リチウム化合物との反応性が悪化し、目的とするリチウムニッケルコバルトチタン複合酸化物を得ることができない。また、３００℃よりも低いと、ニッケルコバルトチタン水酸化物がニッケルコバルトチタン酸化物へ変化する温度に至らないため、チタンの拡散が十分でなく、また同時に、一次粒子の粒成長が進まないため、本発明のリチウムニッケルコバルトチタン複合酸化物が得られない。熱処理は、二次粒子を形成している一次粒子の粒成長を促進して、比表面積を低減させるとともに、一次粒子同士の隙間を低減して、タップ密度を向上させる効果を最大限発揮するために行われる。 The obtained nickel cobalt titanium composite hydroxide needs to be heat-treated at a temperature of 300 ° C. or higher and lower than 900 ° C. The heat treatment temperature is more preferably 750 ° C to 800 ° C. When the heat treatment temperature is 900 ° C. or higher, the grain growth after the composite hydroxide is changed to an oxide is remarkable, the reactivity with the lithium compound is deteriorated, and the intended lithium nickel cobalt titanium composite oxide is obtained. I can't. Also, if the temperature is lower than 300 ° C., the temperature at which nickel cobalt titanium hydroxide changes to nickel cobalt titanium oxide is not reached, so that titanium is not sufficiently diffused, and at the same time, primary particle growth does not proceed. The lithium nickel cobalt titanium composite oxide of the present invention cannot be obtained. Heat treatment promotes grain growth of primary particles forming secondary particles, reduces specific surface area, reduces gaps between primary particles, and maximizes the effect of improving tap density To be done.
本発明の正極活物質は、リチウム化合物と、前述の方法で得られたニッケルコバルトチタン複合酸化物Ｎｉ1-x-yＣｏxＴｉyＯ2を、それぞれ所定量混合し、酸素気流中で６５０℃以上、８５０℃以下の温度で、１０時間〜２０時間程度、焼成することによって合成することができる。６５０℃より低温であると、リチウム化合物との反応が十分に進まず、所望の層状構造をもったリチウムニッケルコバルトチタン複合酸化物を合成することが難しくなる。また、８５０℃を超えると、リチウム層にニッケルが、ニッケル層にリチウムが混入して層状構造が乱れ、３ａサイトにおけるリチウム以外の金属イオンのサイト占有率が２％より大きくなってしまい、リチウムのサイトである３ａサイトに金属イオンの混入率が高くなり、リチウムイオンの拡散パスが阻害され、得られた正極を用いた電池は、初期容量や出力が低下してしまうことから、好ましくない。 The positive electrode active material of the present invention is a mixture of a lithium compound and a nickel cobalt titanium composite oxide Ni 1-xy Co x Ti y O 2 obtained by the above-described method, respectively, and 650 ° C. or higher in an oxygen stream. Can be synthesized by firing at a temperature of 850 ° C. or lower for about 10 to 20 hours. When the temperature is lower than 650 ° C., the reaction with the lithium compound does not proceed sufficiently, and it becomes difficult to synthesize a lithium nickel cobalt titanium composite oxide having a desired layered structure. When the temperature exceeds 850 ° C., nickel is mixed into the lithium layer, lithium is mixed into the nickel layer, and the layered structure is disturbed, and the site occupancy of metal ions other than lithium at the 3a site becomes larger than 2%. Since the mixing rate of metal ions at the 3a site, which is the site, is increased, the lithium ion diffusion path is hindered, and the battery using the obtained positive electrode is not preferable because the initial capacity and output are reduced.
また、得られた正極活物質の粒度分布のＤ５０は、４．５μｍ〜８．１μｍであり、タップ密度は１．５ｇ/ｍｌ以上であることが好ましい。この範囲を外れると、正極を作製するときに、十分、正極活物質を充填できなくなるなど、正極材料として相応しくなくなってしまうからである。 Moreover, D50 of the particle size distribution of the obtained positive electrode active material is 4.5 μm to 8.1 μm, and the tap density is preferably 1.5 g / ml or more. If it is out of this range, it becomes unsuitable as a positive electrode material, for example, when the positive electrode is produced, the positive electrode active material cannot be sufficiently filled.
次に、正極を形成する正極合材およびそれを構成する各材料について説明する。 Next, the positive electrode mixture forming the positive electrode and each material constituting the positive electrode mixture will be described.
前記一般式Ｌｉ1+zＮｉ1-x-yＣｏxＴｉyＯ2（ただし、０．１０≦ｘ≦０．２１、０．０３≦ｙ≦０．０８、−０．０５≦ｚ≦０．１０）で表されるリチウムニッケルコバルトチタン複合酸化物を正極活物質として用いる正極は、例えば、次のようにして作製する。 The general formula Li 1 + z Ni 1-xy Co x Ti y O 2 (where 0.10 ≦ x ≦ 0.21, 0.03 ≦ y ≦ 0.08, −0.05 ≦ z ≦ 0.10) For example, the positive electrode using the lithium nickel cobalt titanium composite oxide represented by (2) is produced as follows.
粉末状の正極活物質、導電材、結着剤とを混合し、さらに必要に応じて活性炭、粘度調整等の目的の溶剤を添加し、混練して、正極合材ペーストを作製する。正極合材ペースト中のそれぞれの混合比も、リチウム二次電池の性能を決定する重要な要素となる。溶剤を除いた固形分の全質量を１００質量％とした場合、一般のリチウム二次電池の正極と同様、正極活物質の含有量を６０〜９５質量％とし、導電材の含有量を１〜２０質量％とし、結着剤の含有量を１〜２０質量％とすることが望ましい。 A powdered positive electrode active material, a conductive material, and a binder are mixed, and if necessary, a target solvent such as activated carbon and viscosity adjustment is added and kneaded to prepare a positive electrode mixture paste. Each mixing ratio in the positive electrode mixture paste is also an important factor that determines the performance of the lithium secondary battery. When the total mass of the solid content excluding the solvent is 100% by mass, the content of the positive electrode active material is 60 to 95% by mass as in the case of the positive electrode of a general lithium secondary battery, and the content of the conductive material is 1 to It is desirable that the content is 20% by mass, and the content of the binder is 1 to 20% by mass.
得られた正極合材ペーストを、例えば、アルミニウム箔製の集電体の表面に塗布し、乾燥して、溶剤を飛散させる。必要に応じ、電極密度を高めるべく、ロールプレス等により加圧することもある。このようにして、シート状の正極を作製することができる。シート状の正極は、目的とする電池に応じて適当な大きさに裁断等をして、電池の作製に供することができる。ただし、正極の作製方法は、前記例示のものに限られることなく、他の方法によってもよい。 The obtained positive electrode mixture paste is applied to the surface of a current collector made of, for example, an aluminum foil and dried to disperse the solvent. If necessary, pressurization may be performed by a roll press or the like to increase the electrode density. In this way, a sheet-like positive electrode can be produced. The sheet-like positive electrode can be cut into an appropriate size or the like according to the target battery and used for battery production. However, the method for manufacturing the positive electrode is not limited to the above-described examples, and other methods may be used.
正極の作製にあたって、導電剤としては、例えば、黒鉛（天然黒鉛、人造黒鉛、膨張黒鉛など）や、アセチレンブラック、ケッチェンブラックなどのカーボンブラック系材料などを用いることができる。 In producing the positive electrode, as the conductive agent, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black materials such as acetylene black, ketjen black, and the like can be used.
また、バインダとしては、例えば、ポリフッ化ビニリデン、ポリテトラフルオロエチレン、エチレンプロピレンジエンゴム、フッ素ゴム、スチレンブタジエン、セルロース系樹脂、ポリアクリル酸などを用いることができる。 Examples of the binder that can be used include polyvinylidene fluoride, polytetrafluoroethylene, ethylene propylene diene rubber, fluororubber, styrene butadiene, cellulose resin, and polyacrylic acid.
結着剤は、活物質粒子をつなぎ止める役割を果たすもので、例えば、ポリテトラフルオロエチレン、ポリフッ化ビニリデン、フッ素ゴム等の含フッ素樹脂、ポリプロピレン、ポリエチレン等の熱可塑性樹脂等を用いることができる。必要に応じ、正極活物質、導電材、活性炭を分散させ、結着剤を溶解する溶剤を正極合材に添加する。溶剤としては、具体的には、Ｎ−メチル−２−ピロリドン等の有機溶剤を用いることができる。また、正極合材には、電気二重層容量を増加させるために、活性炭を添加することができる。 The binder plays a role of holding the active material particles, and for example, fluorine-containing resins such as polytetrafluoroethylene, polyvinylidene fluoride, and fluororubber, and thermoplastic resins such as polypropylene and polyethylene can be used. If necessary, a positive electrode active material, a conductive material, and activated carbon are dispersed, and a solvent that dissolves the binder is added to the positive electrode mixture. Specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent. Activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity.
（２）負極
負極には、金属リチウムやリチウム合金等を使用したり、あるいは、リチウムイオンを吸蔵および脱離できる負極活物質に、結着剤を混合し、適当な溶剤を加えてペースト状にした負極合材を、銅等の金属箔集電体の表面に塗布し、乾燥し、必要に応じて電極密度を高めるべく圧縮して形成したものを使用する。
(2) Negative electrode For the negative electrode, metallic lithium or lithium alloy is used, or a negative electrode active material capable of inserting and extracting lithium ions is mixed with a binder, and an appropriate solvent is added to form a paste. The formed negative electrode mixture is applied to the surface of a metal foil current collector such as copper, dried, and compressed to increase the electrode density as necessary.
負極活物質としては、例えば、天然黒鉛、人造黒鉛、フェノール樹脂等の有機化合物焼成体、コークス等の炭素物質の粉状体を用いることができる。この場合、負極結着剤としては、正極同様、ポリフッ化ビニリデン等の含フッ素樹脂等を用いることができ、これらの活物質および結着剤を分散させる溶剤としては、Ｎ−メチル−２−ピロリドン等の有機溶剤を用いることができる。 As the negative electrode active material, for example, natural graphite, artificial graphite, a fired organic compound such as phenol resin, or a powdery carbon material such as coke can be used. In this case, as the negative electrode binder, a fluorine-containing resin such as polyvinylidene fluoride can be used as in the case of the positive electrode, and N-methyl-2-pyrrolidone is used as a solvent for dispersing these active materials and the binder. An organic solvent such as can be used.
（３）セパレータ
正極と負極との間には、セパレータを挟み込んで配置する。セパレータは、正極と負極とを分離し、電解質を保持するものであり、ポリエチレン、ポリプロピレン等の薄い膜で、微少な孔を多数有する膜を用いることができる。
(3) Separator A separator is interposed between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode and retains the electrolyte, and a thin film such as polyethylene or polypropylene and a film having many minute holes can be used.
（４）非水系電解液
非水系電解液は、支持塩としてのリチウム塩を有機溶媒に溶解したものである。
(4) Non-aqueous electrolyte The non-aqueous electrolyte is obtained by dissolving a lithium salt as a supporting salt in an organic solvent.
有機溶媒としては、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、トリフルオロプロピレンカーボネート等の環状カーボネート、また、ジエチルカーボネート、ジメチルカーボネート、エチルメチルカーボネート、ジプロピルカーボネート等の鎖状カーボネート、さらに、テトラヒドロフラン、２−メチルテトラヒドロフラン、ジメトキシエタン等のエーテル化合物、エチルメチルスルホン、ブタンスルトン等の硫黄化合物、リン酸トリエチル、リン酸トリオクチル等のリン化合物等から選ばれる１種を単独で、あるいは２種以上を混合して用いることができる。 Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; and tetrahydrofuran, 2- One kind selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesultone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc. are used alone or in admixture of two or more. be able to.
支持塩としては、ＬｉＰＦ6、ＬｉＢＦ4、ＬｉＣｌＯ4、ＬｉＡｓＦ6、ＬｉＮ（ＣＦ3ＳＯ2）2等、およびそれらの複合塩を用いることができる。 As the supporting salt, LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , LiN (CF 3 SO 2 ) 2 , or a composite salt thereof can be used.
さらに、非水系電解液は、ラジカル捕捉剤、界面活性剤および難燃剤等を含んでいてもよい。 Furthermore, the non-aqueous electrolyte solution may contain a radical scavenger, a surfactant, a flame retardant, and the like.
（５）電池の形状、構成
以上のように説明してきた正極、負極、セパレータおよび非水系電解液で構成される本発明のリチウム二次電池の形状は、円筒型、積層型等、種々のものとすることができる。
(5) Shape and configuration of battery The shape of the lithium secondary battery of the present invention composed of the positive electrode, the negative electrode, the separator and the non-aqueous electrolyte described above can be various types such as a cylindrical type and a laminated type. It can be.
いずれの形状を採る場合であっても、正極および負極を、セパレータを介して積層させて電極体とし、得られた電極体に、非水系電解液を含浸させ、正極集電体と外部に通ずる正極端子との間、および、負極集電体と外部に通ずる負極端子との間を、集電用リード等を用いて接続し、電池ケースに密閉して、リチウム二次電池を完成させる。 In any case, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolyte and communicated with the positive electrode current collector and the outside. The positive electrode terminal and the negative electrode current collector and the negative electrode terminal communicating with the outside are connected using a current collecting lead or the like and sealed in a battery case to complete a lithium secondary battery.
以下、本発明の一実施例について、図面を参照して詳述する。図１は、電池評価に用いたコイン電池を示す断面図である。 Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view showing a coin battery used for battery evaluation.
（実施例１）
ニッケル：コバルト：チタンのモル比が８１：１５：４となるように、硫酸ニッケルおよび硫酸コバルトの混合溶液と硫酸チタニルの硫酸水溶液を準備し、１２．５％水酸化ナトリウム溶液を反応槽に同時に添加し、ｐＨを１０〜１１の範囲、反応温度を５０℃〜８０℃の範囲内で一定に保ち、共沈法によってニッケルコバルトチタン複合水酸化物からなる粒子を形成させた。
Example 1
A mixed solution of nickel sulfate and cobalt sulfate and a sulfuric acid aqueous solution of titanyl sulfate were prepared so that the molar ratio of nickel: cobalt: titanium was 81: 15: 4, and 12.5% sodium hydroxide solution was simultaneously added to the reaction vessel. Then, the pH was kept in the range of 10 to 11 and the reaction temperature was kept constant in the range of 50 to 80 ° C., and particles composed of nickel cobalt titanium composite hydroxide were formed by coprecipitation method.
その後、反応槽内の水酸化物スラリーを全量回収し、濾過し、水洗後、乾燥し、ニッケルコバルトチタン複合水酸化物の乾燥粉末を得た。さらに、電気炉を用いて、ニッケルコバルトチタン複合水酸化物を７５０℃で１０時間、熱処理し、ニッケルコバルトチタン複合酸化物を得た。 Thereafter, the entire amount of the hydroxide slurry in the reaction vessel was recovered, filtered, washed with water, and dried to obtain a dry powder of nickel cobalt titanium composite hydroxide. Further, using an electric furnace, the nickel cobalt titanium composite hydroxide was heat-treated at 750 ° C. for 10 hours to obtain a nickel cobalt titanium composite oxide.
得られたニッケルコバルトチタン複合酸化物と市販の水酸化リチウム一水和物（ＦＭＣ社製）とを、ニッケル、コバルトおよびチタンの合計とリチウムの原子比が１：１．０５となるように秤量した後、球状の二次粒子の形骸が維持される程度の強さで、シェーカーミキサー（ＷＡＢ社製ＴＵＲＢＵＬＡ ＴｙｐｅＴ２Ｃ）を用いて十分に混合した。得られた混合物２０ｇを、５ｃｍ×１２ｃｍ×３ｃｍのマグネシア製の焼成容器に装入し、密閉式電気炉を用いて、流量３Ｌ／ｍｉｎの酸素気流中で、昇温速度５℃／ｍｉｎで７３０℃まで昇温して、１０時間焼成した後、室温まで炉冷して、本実施例の正極活物質（Ｌｉ1.05Ｎｉ0.81Ｃｏ0.15Ｔｉ0.04Ｏ2）を得た。 The obtained nickel-cobalt-titanium composite oxide and commercially available lithium hydroxide monohydrate (manufactured by FMC) were weighed so that the atomic ratio of the total of nickel, cobalt and titanium to lithium was 1: 1.05. After that, the mixture was sufficiently mixed using a shaker mixer (TURBULA Type T2C manufactured by WAB) at such a strength that the shape of spherical secondary particles was maintained. 20 g of the obtained mixture was charged into a 5 cm × 12 cm × 3 cm magnesia firing container, and 730 at a heating rate of 5 ° C./min in an oxygen stream at a flow rate of 3 L / min using a sealed electric furnace. After raising the temperature to 0 ° C. and firing for 10 hours, the furnace was cooled to room temperature to obtain a positive electrode active material (Li 1.05 Ni 0.81 Co 0.15 Ti 0.04 O 2 ) of this example.
得られた焼成物をＸ線回折で分析したところ、六方晶系の層状構造を有することを確認した。ＢＥＴ法で測定した比表面積は、０．５０ｍ2／ｇであった。また、タップ密度を蔵持科学器械製作所製振盪比重測定器ＫＲＳ−４０６により測定したところ、１．９４ｇ／ｃｃであった。 When the obtained fired product was analyzed by X-ray diffraction, it was confirmed that it had a hexagonal layered structure. The specific surface area measured by the BET method was 0.50 m 2 / g. Moreover, it was 1.94 g / cc when the tap density was measured by the shaking specific gravity measuring device KRS-406 by Kuramochi Scientific Instruments.
得られた正極活物質の初期容量評価は、以下のようにして行った。 The initial capacity evaluation of the obtained positive electrode active material was performed as follows.
正極活物質の粉末７０質量％に、アセチレンブラック２０質量％およびＰＴＦＥ１０質量％を混合し、ここから１５０ｍｇを取り出してペレットを作製し、正極とした。負極としてリチウム金属を用い、電解液には１ＭのＬｉＣｌＯ4を支持塩とするエチレンカーボネート（ＥＣ）とジエチルカーボネート（ＤＥＣ）の等量混合溶液（富山薬品工業製）を用いた。これらを用いて、露点が−８０℃に管理されたＡｒ雰囲気のグローブボックス中で、図１に一部破断斜視図を示すような２０３２型のコイン電池を作製した。 70% by mass of the positive electrode active material powder was mixed with 20% by mass of acetylene black and 10% by mass of PTFE, and 150 mg was taken out from this to produce a pellet, which was used as the positive electrode. Lithium metal was used as the negative electrode, and an equivalent mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) (made by Toyama Pharmaceutical Co., Ltd.) using 1M LiClO 4 as a supporting salt was used as the electrolyte. Using these, a 2032 type coin battery as shown in a partially broken perspective view in FIG. 1 was fabricated in an Ar atmosphere glove box whose dew point was controlled at −80 ° C.
作製した電池は、２４時間程度放置し、開路電圧ＯＣＶ（Open Circuit Voltage）が安定した後、正極に対する電流密度を０．５ｍＡ／ｃｍ2として、カットオフ電圧４．３Ｖまで充電して、初期充電容量とし、１時間の休止後、カットオフ電圧３．０Ｖまで放電したときの容量を、初期放電容量とした。 The prepared battery is left for about 24 hours, and after the open circuit voltage OCV (Open Circuit Voltage) is stabilized, the current density with respect to the positive electrode is set to 0.5 mA / cm 2 and charged to a cutoff voltage of 4.3 V to perform initial charging. The capacity when the battery was discharged to a cutoff voltage of 3.0 V after a pause of 1 hour was defined as the initial discharge capacity.
正極の安全性の評価は、前述と同様な方法で作製した２０３２型のコイン電池を用いて、以下のように行った。まず、カットオフ電圧４．５ＶまでＣＣＣＶ充電（定電流−定電圧充電。最初に、充電が定電流で動作し、それから定電圧で充電を終了するという２つのフェーズの充電過程を用いる充電方法。）した後、短絡しないように注意しながら解体して正極を取り出した。得られた正極を３．０ｍｇ計り取り、電解液を１．３ｍｇ加えて、アルミニウム製測定容器に封入し、示差走査熱量計（ＤＳＣ）（Ｒｉｇａｋｕ社製ＰＴＣ−１０Ａ）を用いて、昇温速度１０℃／ｍｉｎで室温から４００℃までの発熱速度を測定した。 Evaluation of the safety of the positive electrode was performed as follows using a 2032 type coin battery manufactured by the same method as described above. First, CCCV charge up to a cut-off voltage of 4.5 V (constant current-constant voltage charge. First, a charging method using a charging process of two phases in which charging is operated at a constant current and then charging is terminated at a constant voltage. ) And then disassembled with care so as not to short-circuit, and the positive electrode was taken out. 3.0 mg of the obtained positive electrode was weighed out, 1.3 mg of the electrolyte was added, sealed in an aluminum measuring container, and the temperature rising rate was measured using a differential scanning calorimeter (DSC) (PTC-10A manufactured by Rigaku). The heat generation rate from room temperature to 400 ° C. was measured at 10 ° C./min.
得られたリチウムニッケルコバルトチタン複合酸化物の元素分析値、ＢＥＴ法による比表面積、初期放電容量、およびＤＳＣ測定によって得られた発熱速度を、表１に示す。 Table 1 shows the elemental analysis values, specific surface area by BET method, initial discharge capacity, and heat generation rate obtained by DSC measurement of the obtained lithium nickel cobalt titanium composite oxide.
（実施例２）
ニッケルコバルトチタン複合水酸化物の熱処理温度を７８０℃とした以外は、実施例１と同様に正極活物質を作製した。得られた正極活物質をＸ線回折で分析したところ、六方晶系の層状構造を有することを確認した。ＢＥＴ法で測定した比表面積は０．４８ｍ2／ｇであった。また、タップ密度は、１．９５ｇ／ｃｃであった。
(Example 2)
A positive electrode active material was produced in the same manner as in Example 1 except that the heat treatment temperature of the nickel cobalt titanium composite hydroxide was 780 ° C. When the obtained positive electrode active material was analyzed by X-ray diffraction, it was confirmed that it had a hexagonal layered structure. The specific surface area measured by the BET method was 0.48 m 2 / g. The tap density was 1.95 g / cc.
初期容量評価は、実施例１と同様に行った。得られたリチウムニッケルコバルトチタン複合酸化物の元素分析値、ＢＥＴ法による比表面積、初期放電容量、およびＤＳＣ測定によって得られた発熱速度を、表１に示す。 The initial capacity evaluation was performed in the same manner as in Example 1. Table 1 shows the elemental analysis values, specific surface area by BET method, initial discharge capacity, and heat generation rate obtained by DSC measurement of the obtained lithium nickel cobalt titanium composite oxide.
（実施例３）
ニッケルコバルトチタン複合水酸化物の熱処理温度を８００℃とした以外は、実施例１と同様に正極活物質を作製した。得られた正極活物質をＸ線回折で分析したところ、六方晶系の層状構造を有することを確認した。ＢＥＴ法で測定した比表面積は０．４５ｍ2／ｇであった。また、タップ密度は、１．９８ｇ／ｃｃであった。
(Example 3)
A positive electrode active material was produced in the same manner as in Example 1 except that the heat treatment temperature of the nickel cobalt titanium composite hydroxide was 800 ° C. When the obtained positive electrode active material was analyzed by X-ray diffraction, it was confirmed that it had a hexagonal layered structure. The specific surface area measured by the BET method was 0.45 m 2 / g. The tap density was 1.98 g / cc.
初期容量評価は、実施例１と同様に行った。得られたリチウムニッケルコバルトチタン複合酸化物の元素分析値、ＢＥＴ法による比表面積、初期放電容量、およびＤＳＣ測定によって得られた発熱速度を、表１に示す。 The initial capacity evaluation was performed in the same manner as in Example 1. Table 1 shows the elemental analysis values, specific surface area by BET method, initial discharge capacity, and heat generation rate obtained by DSC measurement of the obtained lithium nickel cobalt titanium composite oxide.
（実施例４）
ニッケルコバルトチタン複合水酸化物の熱処理温度を８５０℃とした以外は、実施例１と同様に正極活物質を作製した。得られた正極活物質をＸ線回折で分析したところ、六方晶系の層状構造を有することを確認した。ＢＥＴ法で測定した比表面積は０．４０ｍ2／ｇであった。また、タップ密度は、１．９４ｇ／ｃｃであった。
Example 4
A positive electrode active material was produced in the same manner as in Example 1 except that the heat treatment temperature of the nickel cobalt titanium composite hydroxide was 850 ° C. When the obtained positive electrode active material was analyzed by X-ray diffraction, it was confirmed that it had a hexagonal layered structure. The specific surface area measured by the BET method was 0.40 m 2 / g. The tap density was 1.94 g / cc.
初期容量評価は、実施例１と同様に行った。得られたリチウムニッケルコバルトチタン複合酸化物の元素分析値、ＢＥＴ法による比表面積、初期放電容量、およびＤＳＣ測定によって得られた発熱速度を、表１に示す。 The initial capacity evaluation was performed in the same manner as in Example 1. Table 1 shows the elemental analysis values, specific surface area by BET method, initial discharge capacity, and heat generation rate obtained by DSC measurement of the obtained lithium nickel cobalt titanium composite oxide.
（実施例５）
ニッケルコバルトチタン複合水酸化物の熱処理温度を８００℃とし、焼成温度を８００℃とした以外は、実施例１と同様に正極活物質を作製した。得られた正極活物質をＸ線回折で分析したところ、六方晶系の層状構造を有することを確認した。ＢＥＴ法で測定した比表面積は０．３５ｍ2／ｇであった。また、タップ密度は、１．９７ｇ／ｃｃであった。
(Example 5)
A positive electrode active material was produced in the same manner as in Example 1 except that the heat treatment temperature of the nickel cobalt titanium composite hydroxide was 800 ° C. and the firing temperature was 800 ° C. When the obtained positive electrode active material was analyzed by X-ray diffraction, it was confirmed that it had a hexagonal layered structure. The specific surface area measured by the BET method was 0.35 m 2 / g. The tap density was 1.97 g / cc.
初期容量評価は、実施例１と同様に行った。得られたリチウムニッケルコバルトチタン複合酸化物の元素分析値、ＢＥＴ法による比表面積、初期放電容量、およびＤＳＣ測定によって得られた発熱速度を、表１に示す。 The initial capacity evaluation was performed in the same manner as in Example 1. Table 1 shows the elemental analysis values, specific surface area by BET method, initial discharge capacity, and heat generation rate obtained by DSC measurement of the obtained lithium nickel cobalt titanium composite oxide.
（実施例６）
ニッケルコバルトチタン複合水酸化物の熱処理温度を８５０℃とし、焼成温度を８００℃とした以外は、実施例１と同様に正極活物質を作製した。得られた正極活物質をＸ線回折で分析したところ、六方晶系の層状構造を有することを確認した。ＢＥＴ法で測定した比表面積は０．３２ｍ2／ｇであった。また、タップ密度は、２．００ｇ／ｃｃであった。
(Example 6)
A positive electrode active material was produced in the same manner as in Example 1 except that the heat treatment temperature of the nickel cobalt titanium composite hydroxide was 850 ° C. and the firing temperature was 800 ° C. When the obtained positive electrode active material was analyzed by X-ray diffraction, it was confirmed that it had a hexagonal layered structure. The specific surface area measured by the BET method was 0.32 m 2 / g. The tap density was 2.00 g / cc.
初期容量評価は、実施例１と同様に行った。得られたリチウムニッケルコバルトチタン複合酸化物の元素分析値、ＢＥＴ法による比表面積、初期放電容量、およびＤＳＣ測定によって得られた発熱速度を、表１に示す。 The initial capacity evaluation was performed in the same manner as in Example 1. Table 1 shows the elemental analysis values, specific surface area by BET method, initial discharge capacity, and heat generation rate obtained by DSC measurement of the obtained lithium nickel cobalt titanium composite oxide.
（実施例７）
ニッケルコバルトチタン複合水酸化物の熱処理温度を３００℃とした以外は、実施例１と同様に正極活物質を作製した。得られた正極活物質をＸ線回折で分析したところ、六方晶系の層状構造を有することを確認した。ＢＥＴ法で測定した比表面積は０．５７ｍ2／ｇであった。また、タップ密度は、１．８８ｇ／ｃｃであった。
(Example 7)
A positive electrode active material was produced in the same manner as in Example 1 except that the heat treatment temperature of the nickel cobalt titanium composite hydroxide was 300 ° C. When the obtained positive electrode active material was analyzed by X-ray diffraction, it was confirmed that it had a hexagonal layered structure. The specific surface area measured by the BET method was 0.57 m 2 / g. The tap density was 1.88 g / cc.
初期容量評価は、実施例１と同様に行った。得られたリチウムニッケルコバルトチタン複合酸化物の元素分析値、ＢＥＴ法による比表面積、初期放電容量、およびＤＳＣ測定によって得られた発熱速度を、表１に示す。 The initial capacity evaluation was performed in the same manner as in Example 1. Table 1 shows the elemental analysis values, specific surface area by BET method, initial discharge capacity, and heat generation rate obtained by DSC measurement of the obtained lithium nickel cobalt titanium composite oxide.
（比較例１）
ニッケル：コバルト：チタンのモル比が８１：１５：４となるように、硫酸ニッケルおよび硫酸コバルトの混合溶液と硫酸チタニルの硫酸水溶液を準備し、１２．５％水酸化ナトリウム溶液を反応槽に同時に添加し、ｐＨを１０〜１１の範囲、反応温度を５０℃〜８０℃の範囲で一定に保ち、共沈法によってニッケルコバルトチタン複合水酸化物からなる粒子を形成させた。
(Comparative Example 1)
A mixed solution of nickel sulfate and cobalt sulfate and a sulfuric acid aqueous solution of titanyl sulfate were prepared so that the molar ratio of nickel: cobalt: titanium was 81: 15: 4, and 12.5% sodium hydroxide solution was simultaneously added to the reaction vessel. The mixture was added, and the pH was kept in the range of 10 to 11 and the reaction temperature was kept constant in the range of 50 to 80 ° C., and particles composed of nickel cobalt titanium composite hydroxide were formed by the coprecipitation method.
その後、反応槽内の水酸化物スラリーを全量回収し、濾過し、水洗後、乾燥し、ニッケルコバルトチタン複合水酸化物の乾燥粉末を得た。 Thereafter, the entire amount of the hydroxide slurry in the reaction vessel was recovered, filtered, washed with water, and dried to obtain a dry powder of nickel cobalt titanium composite hydroxide.
得られたニッケルコバルトチタン複合水酸化物と市販の水酸化リチウム一水和物（ＦＭＣ社製）とを、ニッケル、コバルトおよびチタンの合計とリチウムの原子比が１：１．０５となるように秤量した後、球状の二次粒子の形骸が維持される程度の強さで、シェ−カーミキサー（ＷＡＢ社製ＴＵＲＢＵＬＡ ＴｙｐｅＴ２Ｃ）を用いて十分に混合した。得られた混合物２０ｇを、５ｃｍ×１２ｃｍ×３ｃｍのマグネシア製の焼成容器に装入し、密閉式電気炉を用いて、流量３Ｌ／ｍｉｎの酸素気流中で、昇温速度５℃／ｍｉｎで７３０℃まで昇温して、１０時間焼成した後、室温まで炉冷して、本比較例の正極活物質を得た。 The obtained nickel-cobalt-titanium composite hydroxide and commercially available lithium hydroxide monohydrate (manufactured by FMC) were so added that the atomic ratio of lithium to nickel, cobalt and titanium and lithium was 1: 1.05. After weighing, the mixture was sufficiently mixed using a shaker mixer (TURBULA Type T2C manufactured by WAB) at such a strength that the shape of spherical secondary particles was maintained. 20 g of the obtained mixture was charged into a 5 cm × 12 cm × 3 cm magnesia firing container, and 730 at a heating rate of 5 ° C./min in an oxygen stream at a flow rate of 3 L / min using a sealed electric furnace. After raising the temperature to 0 ° C. and firing for 10 hours, the furnace was cooled to room temperature to obtain the positive electrode active material of this comparative example.
得られた正極活物質をＸ線回折で分析したところ、六方晶系の層状構造を有することを確認した。ＢＥＴ法で測定した比表面積は、０．９３ｍ2／ｇであった。また、タップ密度は、１．４６ｇ／ｃｃであった。 When the obtained positive electrode active material was analyzed by X-ray diffraction, it was confirmed that it had a hexagonal layered structure. The specific surface area measured by the BET method was 0.93 m 2 / g. The tap density was 1.46 g / cc.
初期容量評価は、実施例１と同様に行った。得られたリチウムニッケルコバルトチタン複合酸化物の元素分析値、ＢＥＴ法による比表面積、初期放電容量、およびＤＳＣ測定によって得られた発熱速度を、表１に示す。 The initial capacity evaluation was performed in the same manner as in Example 1. Table 1 shows the elemental analysis values, specific surface area by BET method, initial discharge capacity, and heat generation rate obtained by DSC measurement of the obtained lithium nickel cobalt titanium composite oxide.
（比較例２）
焼成温度を８００℃とした以外は、比較例１と同様に正極活物質を作製した。
(Comparative Example 2)
A positive electrode active material was produced in the same manner as in Comparative Example 1 except that the firing temperature was 800 ° C.
得られた正極活物質をＸ線回折で分析したところ、六方晶系の層状構造を有することを確認した。ＢＥＴ法で測定した比表面積は０．８３ｍ2／ｇであった。また、タップ密度は、１．７６ｇ／ｃｃであった。 When the obtained positive electrode active material was analyzed by X-ray diffraction, it was confirmed that it had a hexagonal layered structure. The specific surface area measured by the BET method was 0.83 m 2 / g. The tap density was 1.76 g / cc.
初期容量評価は、実施例１と同様に行った。得られたリチウムニッケルコバルトチタン複合酸化物の元素分析値、ＢＥＴ法による比表面積、初期放電容量、およびＤＳＣ測定によって得られた発熱速度を、表１に示す。 The initial capacity evaluation was performed in the same manner as in Example 1. Table 1 shows the elemental analysis values, specific surface area by BET method, initial discharge capacity, and heat generation rate obtained by DSC measurement of the obtained lithium nickel cobalt titanium composite oxide.
（比較例３）
ニッケルコバルトチタン複合水酸化物の熱処理温度を９００℃とした以外は、実施例１と同様に正極活物質を作製した。得られた正極活物質をＸ線回折で分析したところ、六方晶系の層状構造を有することを確認した。ＢＥＴ法で測定した比表面積は０．７１ｍ2／ｇであった。また、タップ密度は、１．９７ｇ／ｃｃであった。
(Comparative Example 3)
A positive electrode active material was prepared in the same manner as in Example 1 except that the heat treatment temperature of the nickel cobalt titanium composite hydroxide was set to 900 ° C. When the obtained positive electrode active material was analyzed by X-ray diffraction, it was confirmed that it had a hexagonal layered structure. The specific surface area measured by the BET method was 0.71 m 2 / g. The tap density was 1.97 g / cc.
初期容量評価は、実施例１と同様に行った。得られたリチウムニッケルコバルトチタン複合酸化物の元素分析値、ＢＥＴ法による比表面積、初期放電容量、およびＤＳＣ測定によって得られた発熱速度を、表１に示す。 The initial capacity evaluation was performed in the same manner as in Example 1. Table 1 shows the elemental analysis values, specific surface area by BET method, initial discharge capacity, and heat generation rate obtained by DSC measurement of the obtained lithium nickel cobalt titanium composite oxide.
（比較例４）
ニッケルコバルトチタン複合水酸化物の熱処理温度を１０００℃とした以外は、実施例１と同様に正極活物質を作製した。得られた正極活物質をＸ線回折で分析したところ、六方晶系の層状構造を有することを確認した。ＢＥＴ法で測定した比表面積は０．７３ｍ2／ｇであった。また、タップ密度は、２．０３ｇ／ｃｃであった。
(Comparative Example 4)
A positive electrode active material was produced in the same manner as in Example 1 except that the heat treatment temperature of the nickel cobalt titanium composite hydroxide was 1000 ° C. When the obtained positive electrode active material was analyzed by X-ray diffraction, it was confirmed that it had a hexagonal layered structure. The specific surface area measured by the BET method was 0.73 m 2 / g. The tap density was 2.03 g / cc.
初期容量評価は、実施例１と同様に行った。得られたリチウムニッケルコバルトチタン複合酸化物の元素分析値、ＢＥＴ法による比表面積、初期放電容量、およびＤＳＣ測定によって得られた発熱速度を、表１に示す。 The initial capacity evaluation was performed in the same manner as in Example 1. Table 1 shows the elemental analysis values, specific surface area by BET method, initial discharge capacity, and heat generation rate obtained by DSC measurement of the obtained lithium nickel cobalt titanium composite oxide.
（比較例５）
ニッケルコバルトチタン複合水酸化物の熱処理温度を１１００℃とした以外は、実施例１と同様に正極活物質を作製した。得られた正極活物質をＸ線回折で分析したところ、六方晶系の層状構造を有することを確認した。ＢＥＴ法で測定した比表面積は０．６８ｍ2／ｇであった。また、タップ密度は、２．５４ｇ／ｃｃであった。
(Comparative Example 5)
A positive electrode active material was produced in the same manner as in Example 1 except that the heat treatment temperature of the nickel cobalt titanium composite hydroxide was 1100 ° C. When the obtained positive electrode active material was analyzed by X-ray diffraction, it was confirmed that it had a hexagonal layered structure. The specific surface area measured by the BET method was 0.68 m 2 / g. The tap density was 2.54 g / cc.
初期容量評価は、実施例１と同様に行った。得られたリチウムニッケルコバルトチタン複合酸化物の元素分析値、ＢＥＴ法による比表面積、初期放電容量、およびＤＳＣ測定によって得られた発熱速度を、表１に示す。 The initial capacity evaluation was performed in the same manner as in Example 1. Table 1 shows the elemental analysis values, specific surface area by BET method, initial discharge capacity, and heat generation rate obtained by DSC measurement of the obtained lithium nickel cobalt titanium composite oxide.
（比較例６）
ニッケルコバルトチタン複合水酸化物の熱処理温度を２５０℃とした以外は、実施例１と同様に正極活物質を作製した。得られた正極活物質をＸ線回折で分析したところ、六方晶系の層状構造を有することを確認した。ＢＥＴ法で測定した比表面積は０．８８ｍ2／ｇであった。また、タップ密度は、１．７２ｇ／ｃｃであった。
(Comparative Example 6)
A positive electrode active material was prepared in the same manner as in Example 1 except that the heat treatment temperature of the nickel cobalt titanium composite hydroxide was 250 ° C. When the obtained positive electrode active material was analyzed by X-ray diffraction, it was confirmed that it had a hexagonal layered structure. The specific surface area measured by the BET method was 0.88 m 2 / g. The tap density was 1.72 g / cc.
初期容量評価は、実施例１と同様に行った。得られたリチウムニッケルコバルトチタン複合酸化物の元素分析値、ＢＥＴ法による比表面積、初期放電容量、およびＤＳＣ測定によって得られた発熱速度を、表１に示す。 The initial capacity evaluation was performed in the same manner as in Example 1. Table 1 shows the elemental analysis values, specific surface area by BET method, initial discharge capacity, and heat generation rate obtained by DSC measurement of the obtained lithium nickel cobalt titanium composite oxide.
［評価］
表１に示すように、実施例１〜７で得られたリチウムニッケルコバルトチタン複合酸化物は、リチウムニッケルコバルトチタン複合水酸化物に熱処理を加えて得ているため、二次粒子を形成している一次粒子が成長している。そのため、ＢＥＴ法による比表面積が低減し、０．６ｍ2／ｇ以下となっていることがわかる。また、タップ密度も、一次粒子どうしの焼結が進んでいるために向上し、１．８５ｇ／ｃｃ以上を達成している。
[Evaluation]
As shown in Table 1, since the lithium nickel cobalt titanium composite oxide obtained in Examples 1 to 7 was obtained by applying heat treatment to the lithium nickel cobalt titanium composite hydroxide, secondary particles were formed. Primary particles are growing. Therefore, it can be seen that the specific surface area by the BET method is reduced to 0.6 m 2 / g or less. Further, the tap density is also improved because the primary particles are being sintered, and is 1.85 g / cc or more.
比表面積が低減したその結果、充電電極を加熱した場合に、電解液との反応面積が低減して電解液の分解反応が抑制され、発熱速度が抑えられている。たと考えられる。また、初期放電容量も１８０ｍＡｈ／ｇを超え、リチウムコバルト複合酸化物（ＬｉＣｏＯ2）に代わる新たな電池材料として使用可能な材料であることがわかる。 As a result of reducing the specific surface area, when the charging electrode is heated, the reaction area with the electrolytic solution is reduced, the decomposition reaction of the electrolytic solution is suppressed, and the heat generation rate is suppressed. It is thought. In addition, the initial discharge capacity exceeds 180 mAh / g, and it can be seen that this is a material that can be used as a new battery material in place of lithium cobalt composite oxide (LiCoO 2 ).
一方、比較例１および２のように、ニッケルコバルトチタン複合水酸化物を熱処理せずに、該水酸化物とリチウム化合物を混合し、熱処理することにより、リチウムニッケルコバルトチタン複合酸化物を得た場合には、タップ密度が１．８ｇ／ｃｃ以下と低くなっており、容量とタップ密度との積から計算される単位体積当たりの放電容量は実施例と比較して大きく低下している。また、一次粒子同士の焼結が進んでおらず、比表面積が大きくなってしまっているために、電解液との接触面積が大きく、反応性が大きくなって分解反応が促進され、電池の安全性で問題があるといえる。 On the other hand, as in Comparative Examples 1 and 2, the nickel-cobalt-titanium composite hydroxide was mixed with the hydroxide and the lithium compound without being heat-treated to obtain a lithium-nickel-cobalt-titanium composite oxide. In this case, the tap density is as low as 1.8 g / cc or less, and the discharge capacity per unit volume calculated from the product of the capacity and the tap density is greatly reduced as compared with the example. In addition, the sintering of primary particles has not progressed and the specific surface area has increased, so the contact area with the electrolyte is large, the reactivity is increased, the decomposition reaction is promoted, and the battery safety is increased. It can be said that there is a problem with sex.
また、比較例３〜５のように、ニッケルコバルトチタン複合水酸化物の熱処理温度を９００℃以上にした場合は、焼成後の正極活物質が焼結して固くなり、製品としては粉砕が必要になるため、粉砕工程を加えた結果、比表面積が増大している上、初期放電容量の低下も大きかった。 In addition, when the heat treatment temperature of the nickel cobalt titanium composite hydroxide is set to 900 ° C. or more as in Comparative Examples 3 to 5, the fired positive electrode active material is sintered and hardened, and the product needs to be pulverized. Therefore, as a result of adding the pulverization step, the specific surface area was increased and the initial discharge capacity was greatly reduced.
さらに、比較例６のように、ニッケルコバルトチタン複合水酸化物の熱処理温度を３００℃未満にすると、一次粒子の粒成長が十分でないため、比表面積が増大し、発熱速度が抑えられていない。 Further, as in Comparative Example 6, when the heat treatment temperature of the nickel cobalt titanium composite hydroxide is less than 300 ° C., the grain growth of the primary particles is not sufficient, so that the specific surface area increases and the heat generation rate is not suppressed.
したがって、ニッケルコバルトチタン複合水酸化物の熱処理温度は、３００℃以上、９００℃未満とすることが必要であることがわかる。 Therefore, it can be seen that the heat treatment temperature of the nickel cobalt titanium composite hydroxide needs to be 300 ° C. or higher and lower than 900 ° C.
安全性に優れていながら、高い初期容量を有しているという本発明の非水系電解質二次電池のメリットを活かすためには、常に高容量を要求される小型携帯電子機器の電源に好適である。 In order to take advantage of the non-aqueous electrolyte secondary battery of the present invention that has a high initial capacity while being excellent in safety, it is suitable for a power source of a small portable electronic device that always requires a high capacity. .
また、電気自動車用の電源においては、電池の大型化による安全性の確保の難しさと、より高度な安全性を確保するための高価な保護回路が必要不可欠である。これに対して、本発明のリチウムイオン二次電池は、優れた安全性を有しているため、安全性の確保が容易になるばかりでなく、高価な保護回路を簡略化し、より低コストにできるという点において、電気自動車用電源としても好適である。なお、本発明は、純粋に電気エネルギーで駆動する電気自動車用の電源のみならず、ガソリンエンジン、ディーゼルエンジン等の燃焼機関と併用するいわゆるハイブリッド車用の電源としても用いることができる。 Further, in a power source for an electric vehicle, it is indispensable to ensure safety by increasing the size of the battery and an expensive protection circuit for ensuring higher safety. On the other hand, since the lithium ion secondary battery of the present invention has excellent safety, not only is it easy to ensure safety, but also an expensive protection circuit is simplified to lower costs. In terms of being able to do so, it is also suitable as a power source for electric vehicles. The present invention can be used not only as a power source for an electric vehicle driven purely by electric energy but also as a power source for a so-called hybrid vehicle used in combination with a combustion engine such as a gasoline engine or a diesel engine.
１ リチウム金属負極
２ セパレータ（電解液含浸）
３ 正極（評価用電極）
４ ガスケット
５ 負極缶
６ 正極缶
７ 集電体
1 Lithium metal negative electrode 2 Separator (electrolyte impregnation)
3 Positive electrode (Evaluation electrode)
4
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